fix(notes): add company_notes.updated_at, drop createdAt substitution

company_notes was missing updated_at — every other notes table has it,
and notes.service.ts substituted created_at into the response shape so
callers wouldn't notice. Add the column (defaulted + backfilled to
created_at for existing rows), wire the update path to set it on
edit, and drop the substitution from the read + edit handlers.

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

src/lib/db/migrations/0048_company_notes_updated_at.sql

@@ -0,0 +1,7 @@
+-- Add updated_at to company_notes so the notes service can return a real
+-- modified timestamp (was substituting created_at). Backfill updated_at
+-- to created_at for existing rows so they read as "never modified".
+ALTER TABLE "company_notes"
+  ADD COLUMN IF NOT EXISTS "updated_at" timestamp with time zone NOT NULL DEFAULT now();
+
+UPDATE "company_notes" SET "updated_at" = "created_at";