feat: @mosaic/coord — migrate from v0, gateway integration (P2-005)

Migrate the orchestration coordination package from v0 with full
file-based mission/task lifecycle management. Adds gateway REST API
at /api/coord/* and agent tools for coord queries.

Package modules:
- types: Mission, task, session, milestone type definitions
- mission: Create, load, save missions with atomic file writes
- tasks-file: TASKS.md markdown table parsing/generation with file locking
- runner: Task execution subprocess spawning with session locks
- status: Mission and task status queries

Gateway integration:
- CoordModule with CoordService wrapping coord functions
- CoordController exposing status/tasks/task-detail endpoints
- Agent tools: coord_mission_status, coord_list_tasks, coord_task_detail

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

apps/gateway/src/coord/coord.controller.ts

@@ -0,0 +1,31 @@
+import { Controller, Get, NotFoundException, Param, Query, UseGuards } from '@nestjs/common';
+import { AuthGuard } from '../auth/auth.guard.js';
+import { CoordService } from './coord.service.js';
+
+@Controller('api/coord')
+@UseGuards(AuthGuard)
+export class CoordController {
+  constructor(private readonly coordService: CoordService) {}
+
+  @Get('status')
+  async missionStatus(@Query('projectPath') projectPath?: string) {
+    const resolvedPath = projectPath ?? process.cwd();
+    const status = await this.coordService.getMissionStatus(resolvedPath);
+    if (!status) throw new NotFoundException('No active coord mission found');
+    return status;
+  }
+
+  @Get('tasks')
+  async listTasks(@Query('projectPath') projectPath?: string) {
+    const resolvedPath = projectPath ?? process.cwd();
+    return this.coordService.listTasks(resolvedPath);
+  }
+
+  @Get('tasks/:taskId')
+  async taskStatus(@Param('taskId') taskId: string, @Query('projectPath') projectPath?: string) {
+    const resolvedPath = projectPath ?? process.cwd();
+    const detail = await this.coordService.getTaskStatus(resolvedPath, taskId);
+    if (!detail) throw new NotFoundException(`Task ${taskId} not found in coord mission`);
+    return detail;
+  }
+}