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/migrations/0087_interest_use_yacht_dims.sql

@@ -0,0 +1,11 @@
+-- 0087_interest_use_yacht_dims.sql
+-- Adds a per-interest toggle so the berth recommender can read the
+-- linked yacht's dimensions instead of the rep-entered `desired_*`
+-- values. Defaults to false so existing data continues to use the
+-- desired-dims path the recommender has always used.
+--
+-- Per docs/superpowers/audits/alpha-uat-master.md Bucket 3 #1:
+-- "Interest dimensions: dual-source model".
+
+ALTER TABLE interests
+  ADD COLUMN IF NOT EXISTS use_yacht_dimensions boolean NOT NULL DEFAULT false;