feat(db): m:m interest_berths junction + role flags

Introduces the multi-berth interest model from plan §3.1: a junction
between interests and berths with three role flags so the same berth
can be linked as the primary deal target, an EOI-bundle inclusion,
or a "just exploring" link without conflating semantics.

- 0028 schema migration creates interest_berths with the unique
  partial index "≤1 primary per interest", a unique compound on
  (interest_id, berth_id), and indexes for the public-map "under
  offer" lookup (where is_specific_interest=true).
- Same migration adds desired_length_ft / desired_width_ft /
  desired_draft_ft to interests for the recommender.
- Same migration runs the Phase 2 data migration: every interest
  with a non-null berth_id gets one junction row marked
  is_primary=true, is_specific_interest=true, and is_in_eoi_bundle =
  (eoi_status='signed'). Pre-flight check halts on dangling FKs
  (§14.3 critical case).
- New service src/lib/services/interest-berths.service.ts owns reads
  + writes of the junction. getPrimaryBerth / getPrimaryBerthsForInterests
  feed list pages; upsertInterestBerth demotes the prior primary in
  the same transaction so the unique index is never violated.
- interests.berth_id stays in place this commit so existing callers
  keep working; Phase 2b migrates them onto the helper service and a
  later migration drops the column.

53 dev rows seeded into the junction; tests still green at 996.

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

src/lib/db/migrations/0028_interest_berths_junction.sql

@@ -0,0 +1,61 @@
+CREATE TABLE "interest_berths" (
+	"id" text PRIMARY KEY NOT NULL,
+	"interest_id" text NOT NULL,
+	"berth_id" text NOT NULL,
+	"is_primary" boolean DEFAULT false NOT NULL,
+	"is_specific_interest" boolean DEFAULT true NOT NULL,
+	"is_in_eoi_bundle" boolean DEFAULT false NOT NULL,
+	"eoi_bypass_reason" text,
+	"eoi_bypassed_by" text,
+	"eoi_bypassed_at" timestamp with time zone,
+	"added_by" text,
+	"added_at" timestamp with time zone DEFAULT now() NOT NULL,
+	"notes" text
+);
+--> statement-breakpoint
+ALTER TABLE "interests" ADD COLUMN "desired_length_ft" numeric;--> statement-breakpoint
+ALTER TABLE "interests" ADD COLUMN "desired_width_ft" numeric;--> statement-breakpoint
+ALTER TABLE "interests" ADD COLUMN "desired_draft_ft" numeric;--> statement-breakpoint
+ALTER TABLE "interest_berths" ADD CONSTRAINT "interest_berths_interest_id_interests_id_fk" FOREIGN KEY ("interest_id") REFERENCES "public"."interests"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "interest_berths" ADD CONSTRAINT "interest_berths_berth_id_berths_id_fk" FOREIGN KEY ("berth_id") REFERENCES "public"."berths"("id") ON DELETE restrict ON UPDATE no action;--> statement-breakpoint
+CREATE UNIQUE INDEX "idx_ib_interest_berth" ON "interest_berths" USING btree ("interest_id","berth_id");--> statement-breakpoint
+CREATE UNIQUE INDEX "idx_ib_one_primary" ON "interest_berths" USING btree ("interest_id") WHERE "interest_berths"."is_primary" = true;--> statement-breakpoint
+CREATE INDEX "idx_ib_berth" ON "interest_berths" USING btree ("berth_id");--> statement-breakpoint
+CREATE INDEX "idx_ib_specific" ON "interest_berths" USING btree ("berth_id") WHERE "interest_berths"."is_specific_interest" = true;--> statement-breakpoint
+-- Pre-flight: halt if any interests.berth_id points at a row that no
+-- longer exists. The new junction's FK is `restrict`, so a dangling
+-- value would otherwise abort the insert mid-batch with a confusing
+-- error.
+DO $$
+DECLARE
+  orphan_count integer;
+BEGIN
+  SELECT count(*) INTO orphan_count
+  FROM interests i
+  LEFT JOIN berths b ON b.id = i.berth_id
+  WHERE i.berth_id IS NOT NULL
+    AND b.id IS NULL;
+  IF orphan_count > 0 THEN
+    RAISE EXCEPTION 'interests.berth_id has % dangling references; resolve manually before re-running', orphan_count;
+  END IF;
+END $$;--> statement-breakpoint
+-- Migrate existing interest.berth_id values into the junction. Every
+-- pre-existing single-berth link becomes a primary, specific-interest
+-- row. is_in_eoi_bundle = true only when the interest already has a
+-- signed EOI (the legacy "the berth is contractually committed" case).
+INSERT INTO interest_berths (
+  id, interest_id, berth_id,
+  is_primary, is_specific_interest, is_in_eoi_bundle,
+  added_at
+)
+SELECT
+  gen_random_uuid()::text,
+  i.id,
+  i.berth_id,
+  true,
+  true,
+  COALESCE(i.eoi_status = 'signed', false),
+  i.created_at
+FROM interests i
+WHERE i.berth_id IS NOT NULL
+ON CONFLICT (interest_id, berth_id) DO NOTHING;

src/lib/db/migrations/meta/_journal.json

@@ -197,6 +197,13 @@
       "when": 1777939914252,
       "tag": "0027_backfill_nationality_iso_from_phone",
       "breakpoints": true
+    },
+    {
+      "idx": 28,
+      "version": "7",
+      "when": 1777940421236,
+      "tag": "0028_interest_berths_junction",
+      "breakpoints": true
     }
   ]
 }