feat(b3-1): interest dimensions dual-source — yacht dims for the recommender

Per docs/superpowers/audits/alpha-uat-master.md Bucket 3 #1. When a
yacht is linked to the interest the rep can flip a per-interest toggle
so the berth recommender reads dimensions off the yacht record instead
of the rep-entered desired_* columns.

- Migration 0087 + interests.useYachtDimensions boolean (default false).
- Validator (createInterestSchema) accepts the new field; service insert
  + update paths spread it through automatically.
- berth-recommender.service.loadInterestInput dual-source resolution:
  when toggle=true AND yachtId is set AND the yacht has at least one
  measurement on file, the recommender uses the yacht's length / width /
  draft instead of the desired_* values. Falls back to the desired
  columns whenever any precondition fails (no yacht link, toggle off,
  or the yacht carries no measurements). Returned InterestInput gains
  a `dimensionsSource: 'interest' | 'yacht'` trace field.
- Interest form: under the "Berth size desired" section, when a yacht
  is linked, a checkbox surfaces — "Use the linked yacht's dimensions
  for the recommender". When checked, the three dimension inputs grey
  out (DimensionInput gains a `disabled` prop) so the rep can't
  accidentally edit the now-overridden values. Hint text spells out
  the fallback behaviour.

Verified: tsc clean, 1493/1493 vitest, migration applied.

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

src/lib/db/schema/interests.ts

@@ -102,6 +102,12 @@ export const interests = pgTable(
     desiredLengthUnit: text('desired_length_unit').notNull().default('ft'),
     desiredWidthUnit: text('desired_width_unit').notNull().default('ft'),
     desiredDraftUnit: text('desired_draft_unit').notNull().default('ft'),
+    /** Per-interest source-of-truth toggle for the berth recommender.
+     *  When true AND a yacht is linked, the recommender uses the yacht's
+     *  length/width/draft instead of the rep-entered desired_* columns
+     *  on this row. Defaults false so existing data continues to use the
+     *  desired-dims path. Migration 0087. */
+    useYachtDimensions: boolean('use_yacht_dimensions').notNull().default(false),
     archivedAt: timestamp('archived_at', { withTimezone: true }),
     createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
     updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),