feat(cli): command architecture — agents, missions, and gateway-aware prdy

DB schema:
- Extend agents table with projectId, ownerId, systemPrompt, allowedTools,
  skills, isSystem columns and indexes
- Add agentId FK to conversations table with index

Brain:
- New agents repository (findAll, findById, findByName, findByProject,
  findSystem, findAccessible, create, update, remove)
- Wire into Brain interface and createBrain factory

Gateway:
- New AgentConfigsController at /api/agents with full CRUD + ownership guards
- Consolidate /api/missions — user-scoped CRUD replaces old project-ownership
  model, add /api/missions/:id/tasks sub-routes (replaces coord mission-tasks)
- Slim coord controller to file-based endpoints only (agent tool consumption)
- Remove DB-backed methods from CoordService (now handled by Brain repos)
- Wire agentConfigId into AgentService.createSession for DB config merging
- Add agentId field to ChatSocketMessageDto and ChatMessagePayload

CLI:
- New `mosaic agent` command (--list, --new, --show, --update, --delete)
- New `mosaic mission` command (--list, --init, --plan, --update, task sub)
- New `mosaic prdy` gateway-aware wrapper (--init, --update, --project)
- Shared with-auth helper and select-dialog utility
- TUI: accept --agent and --project flags, pass agentId to socket, display
  agent name in top bar
- Gateway API client: add agents, projects, missions, mission-tasks helpers
- Add @clack/prompts dependency
- Refactor sessions commands to use with-auth helper

Types:
- Add agentId to ChatMessagePayload

Tests:
- Update resource-ownership test for user-scoped missions (NotFoundException)

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

packages/db/src/schema.ts

@@ -190,18 +190,32 @@ export const events = pgTable(
   (t) => [index('events_type_idx').on(t.type), index('events_date_idx').on(t.date)],
 );
 
-export const agents = pgTable('agents', {
-  id: uuid('id').primaryKey().defaultRandom(),
-  name: text('name').notNull(),
-  provider: text('provider').notNull(),
-  model: text('model').notNull(),
-  status: text('status', { enum: ['idle', 'active', 'error', 'offline'] })
-    .notNull()
-    .default('idle'),
-  config: jsonb('config'),
-  createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
-  updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
-});
+export const agents = pgTable(
+  'agents',
+  {
+    id: uuid('id').primaryKey().defaultRandom(),
+    name: text('name').notNull(),
+    provider: text('provider').notNull(),
+    model: text('model').notNull(),
+    status: text('status', { enum: ['idle', 'active', 'error', 'offline'] })
+      .notNull()
+      .default('idle'),
+    projectId: uuid('project_id').references(() => projects.id, { onDelete: 'set null' }),
+    ownerId: text('owner_id').references(() => users.id, { onDelete: 'set null' }),
+    systemPrompt: text('system_prompt'),
+    allowedTools: jsonb('allowed_tools').$type<string[]>(),
+    skills: jsonb('skills').$type<string[]>(),
+    isSystem: boolean('is_system').notNull().default(false),
+    config: jsonb('config'),
+    createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+    updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
+  },
+  (t) => [
+    index('agents_project_id_idx').on(t.projectId),
+    index('agents_owner_id_idx').on(t.ownerId),
+    index('agents_is_system_idx').on(t.isSystem),
+  ],
+);
 
 export const tickets = pgTable(
   'tickets',
@@ -243,6 +257,7 @@ export const conversations = pgTable(
       .notNull()
       .references(() => users.id, { onDelete: 'cascade' }),
     projectId: uuid('project_id').references(() => projects.id, { onDelete: 'set null' }),
+    agentId: uuid('agent_id').references(() => agents.id, { onDelete: 'set null' }),
     archived: boolean('archived').notNull().default(false),
     createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
     updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow(),
@@ -250,6 +265,7 @@ export const conversations = pgTable(
   (t) => [
     index('conversations_user_id_idx').on(t.userId),
     index('conversations_project_id_idx').on(t.projectId),
+    index('conversations_agent_id_idx').on(t.agentId),
     index('conversations_archived_idx').on(t.archived),
   ],
 );