feat(db): teams schema, preferences.mutable, projects.ownerType

- Add mutable column to preferences table (distinguishes user-adjustable prefs from enforcements)
- Add teams and team_members tables for multi-member project ownership
- Add teamId and ownerType columns to projects table
- Generate Drizzle migration

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

packages/db/drizzle/meta/_journal.json

@@ -15,6 +15,13 @@
       "when": 1773602195609,
       "tag": "0001_magical_rattler",
       "breakpoints": true
+    },
+    {
+      "idx": 2,
+      "version": "7",
+      "when": 1773625181629,
+      "tag": "0002_nebulous_mimic",
+      "breakpoints": true
     }
   ]
 }