feat(FN-989): add inter-agent messaging system with mailbox UI and CLI commands

- Add Message types (Message, MessageThread, MessageRecipient) and exports to @fusion/core
- Create MessageStore with full CRUD: send, read, delete, inbox, threads, and search
- Add messages table migration (schema v12) with SQLite full-text search support
- Add REST API routes for messaging (CRUD, search, broadcast, unread count)
- Add frontend API client functions for all messaging endpoints
- Build MailboxModal and MessageComposer dashboard components with header integration
- Add CLI message commands (inbox, send, read, delete) with rich output formatting
- Add comprehensive test coverage for MessageStore, CLI commands, and UI components
- Update documentation (CLI STANDALONE.md, dashboard README) with messaging usage

packages/core/src/db.ts

@@ -59,7 +59,7 @@ export function fromJson<T>(json: string | null | undefined): T | undefined {
 
 // ── Schema Definition ────────────────────────────────────────────────
 
-const SCHEMA_VERSION = 11;
+const SCHEMA_VERSION = 12;
 
 function normalizeTaskComments(
   steeringComments: SteeringComment[] | undefined,
@@ -451,7 +451,7 @@ export class Database {
     }
 
     // Future migrations go here:
-    // if (version < 12) { this.applyMigration(12, () => { ... }); }
+    // if (version < 13) { this.applyMigration(13, () => { ... }); }
 
     if (version < 10) {
       this.applyMigration(10, () => {
@@ -467,6 +467,29 @@ export class Database {
         this.addColumnIfMissing("tasks", "planningModelId", "TEXT");
       });
     }
+
+    if (version < 12) {
+      this.applyMigration(12, () => {
+        this.db.exec(`
+          CREATE TABLE IF NOT EXISTS messages (
+            id TEXT PRIMARY KEY,
+            fromId TEXT NOT NULL,
+            fromType TEXT NOT NULL,
+            toId TEXT NOT NULL,
+            toType TEXT NOT NULL,
+            content TEXT NOT NULL,
+            type TEXT NOT NULL,
+            read INTEGER DEFAULT 0,
+            metadata TEXT,
+            createdAt TEXT NOT NULL,
+            updatedAt TEXT NOT NULL
+          )
+        `);
+        this.db.exec(`CREATE INDEX IF NOT EXISTS idxMessagesTo ON messages(toId, toType, read)`);
+        this.db.exec(`CREATE INDEX IF NOT EXISTS idxMessagesFrom ON messages(fromId, fromType)`);
+        this.db.exec(`CREATE INDEX IF NOT EXISTS idxMessagesCreatedAt ON messages(createdAt)`);
+      });
+    }
   }
 
   /**