feat: add project_goals many-to-many join table

Create project_goals join table with composite PK (project_id, goal_id),
backfill from existing projects.goal_id, and update the project service
to read/write through the join table. Shared types now include goalIds
and goals arrays on Project. Legacy goalId column is kept in sync.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -78,6 +78,13 @@
       "when": 1771605173513,
       "tag": "0010_stale_justin_hammer",
       "breakpoints": true
+    },
+    {
+      "idx": 11,
+      "version": "7",
+      "when": 1771616419708,
+      "tag": "0011_windy_corsair",
+      "breakpoints": true
     }
   ]
 }