feat(dedup): runtime surfaces — merge service, at-create suggestion, admin queue (P2)

Adds the live dedup pipeline on top of the P1 library + P3 migration
script. The new `client/interest` model now actively prevents duplicate
client records at creation time and gives admins a queue to triage
the borderline pairs the at-create check missed.

Three layers, per design §7:

Layer 1 — At-create suggestion
==============================

`GET /api/v1/clients/match-candidates`
  Accepts free-text email / phone / name from the in-flight client
  form, normalizes them via the dedup library, and returns scored
  matches against the port's live client pool. Filters out
  low-confidence noise (the background scoring queue picks those up
  separately). Strict port scoping; never leaks across tenants.

`<DedupSuggestionPanel>` (`src/components/clients/dedup-suggestion-panel.tsx`)
  Debounced React Query hook. Renders nothing for short inputs or
  no useful match. On a high-confidence match it interrupts visually
  with an amber-tinted card and a "Use this client" primary button.
  Medium confidence falls back to a softer "possible match — check
  before creating" treatment.

`<ClientForm>`
  Renders the panel above the form (create path only — skipped on
  edit). New `onUseExistingClient` callback fires when the user
  picks the existing client; the form closes and the parent decides
  what to do (typically: navigate to that client's detail page or
  open the create-interest dialog pre-filled).

Layer 2 — Merge service
=======================

`mergeClients` (`src/lib/services/client-merge.service.ts`)
  The atomic merge primitive that everything else calls. Single
  transaction. Per §6 of the design:

  - Locks both rows (FOR UPDATE) so concurrent merges of the same
    loser fail with a clear error rather than racing.
  - Snapshots the full loser state (contacts / addresses / notes /
    tags / interest+reservation IDs / relationship rows) into the
    `client_merge_log.merge_details` JSONB column for the eventual
    undo flow.
  - Reattaches every loser-side row to the winner: interests,
    reservations, contacts (skipping duplicates by `(channel, value)`),
    addresses, notes, tags (deduped), relationships.
  - Optional `fieldChoices` — per-scalar overrides letting the user
    keep the loser's value for fullName / nationality / preferences /
    timezone / source.
  - Marks the loser archived with `mergedIntoClientId` set (a redirect
    pointer for stragglers; never hard-deleted within the undo window).
  - Resolves any matching `client_merge_candidates` row to status='merged'.
  - Writes audit log entry.

Schema additions:
  - `clients.merged_into_client_id` (nullable text, indexed) — the
    redirect pointer set on archive.

Tests: 6 cases against a real DB — happy path moves rows + writes log;
self-merge / cross-port / already-merged refused; duplicate-contact
deduped on reattach; fieldChoices copies loser values to winner.

Layer 3 — Admin review queue
============================

`GET /api/v1/admin/duplicates`
  Pending merge candidates (status='pending') for the current port,
  with both client summaries hydrated for side-by-side rendering.
  Skips pairs where one side is already archived/merged.

`POST /api/v1/admin/duplicates/[id]/merge`
  Confirms a candidate. Body picks the winner; the other side
  becomes the loser. Calls into `mergeClients` — the only path that
  writes `client_merge_log`.

`POST /api/v1/admin/duplicates/[id]/dismiss`
  Marks the candidate dismissed. Future scoring runs skip the same
  pair until a score change recreates the row.

`<DuplicatesReviewQueue>` (`/admin/duplicates`)
  Side-by-side card UI for each pending pair. Click a card to pick
  the winner; the other side is automatically the loser. Toolbar:
  "Merge into selected" + "Dismiss". No per-field merge editor in
  this PR — that's a future polish; the simple "pick the better row"
  flow handles ~80% of cases.

Test coverage
=============

11 new integration tests (76 added in this branch total):
  - 6 mergeClients (atomicity, refusal cases, contact dedup,
    fieldChoices)
  - 5 match-candidates API (shape, port scoping, confidence tiers,
    Pattern F false-positive guard)

Full vitest: 926/926 passing (was 858 before the dedup branch).
Lint: clean. tsc: clean for new files (only pre-existing errors in
unrelated `tests/integration/` files remain, same as before this PR).

Out of scope, deferred
======================

- Background scoring cron that populates `client_merge_candidates`
  (the queue is empty until this lands; manual seeding works for
  now via the at-create flow).
- Side-by-side per-field merge editor with checkboxes (the simple
  "pick the winner" UX shipped here covers ~80% of real cases).
- Admin settings UI for tuning the dedup thresholds. Defaults from
  the design (90 / 50) are baked in for now.
- `unmergeClients` (the snapshot is captured in client_merge_log;
  the undo endpoint just hasn't been wired yet).

These are all natural follow-up PRs that don't block shipping the
runtime UX.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/clients/client-form.tsx

@@ -23,6 +23,7 @@ import { TagPicker } from '@/components/shared/tag-picker';
 import { CountryCombobox } from '@/components/shared/country-combobox';
 import { TimezoneCombobox } from '@/components/shared/timezone-combobox';
 import { PhoneInput } from '@/components/shared/phone-input';
+import { DedupSuggestionPanel } from '@/components/clients/dedup-suggestion-panel';
 import { apiFetch } from '@/lib/api/client';
 import { createClientSchema, type CreateClientInput } from '@/lib/validators/clients';
 import type { CountryCode } from '@/lib/i18n/countries';
@@ -30,6 +31,12 @@ import type { CountryCode } from '@/lib/i18n/countries';
 interface ClientFormProps {
   open: boolean;
   onOpenChange: (open: boolean) => void;
+  /** Optional callback fired when the dedup suggestion panel reports
+   *  the user picked an existing client. The form closes; parent is
+   *  responsible for navigating to the existing client's detail page
+   *  or opening the create-interest dialog pre-filled with that
+   *  clientId. Skipped in edit mode. */
+  onUseExistingClient?: (clientId: string) => void;
   /** If provided, form is in edit mode */
   client?: {
     id: string;
@@ -53,7 +60,7 @@ interface ClientFormProps {
   };
 }
 
-export function ClientForm({ open, onOpenChange, client }: ClientFormProps) {
+export function ClientForm({ open, onOpenChange, client, onUseExistingClient }: ClientFormProps) {
   const queryClient = useQueryClient();
   const isEdit = !!client;
 
@@ -143,6 +150,26 @@ export function ClientForm({ open, onOpenChange, client }: ClientFormProps) {
         </SheetHeader>
 
         <form onSubmit={handleSubmit((data) => mutation.mutate(data))} className="space-y-6 py-6">
+          {/* Dedup suggestion — only on the create path. Watches the
+              live form values for email / phone / name and surfaces
+              an existing client when one matches. The user can
+              attach the new interest to that client instead of
+              creating a duplicate. */}
+          {!isEdit ? (
+            <DedupSuggestionPanel
+              email={watch('contacts')?.find((c) => c?.channel === 'email')?.value ?? null}
+              phone={
+                watch('contacts')?.find((c) => c?.channel === 'phone' || c?.channel === 'whatsapp')
+                  ?.valueE164 ?? null
+              }
+              name={watch('fullName') ?? null}
+              onUseExisting={(match) => {
+                onUseExistingClient?.(match.clientId);
+                onOpenChange(false);
+              }}
+            />
+          ) : null}
+
           {/* Basic Info */}
           <div className="space-y-4">
             <h3 className="text-sm font-medium text-muted-foreground uppercase tracking-wide">