feat: scaffold work queue API

internal/db/migrations/001_initial.sql

@@ -0,0 +1,49 @@
+PRAGMA foreign_keys = ON;
+
+CREATE TABLE IF NOT EXISTS projects (
+  id TEXT PRIMARY KEY,
+  name TEXT NOT NULL,
+  external_ref TEXT,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS work_items (
+  id TEXT PRIMARY KEY,
+  project_id TEXT,
+  type TEXT NOT NULL,
+  description TEXT NOT NULL,
+  payload TEXT,
+  priority INTEGER NOT NULL DEFAULT 3 CHECK(priority BETWEEN 1 AND 5),
+  status TEXT NOT NULL CHECK(status IN ('queued','dispatched','in_progress','blocked','failed','completed','cancelled')),
+  assigned_agent TEXT,
+  created_by TEXT,
+  created_at TEXT NOT NULL,
+  updated_at TEXT NOT NULL,
+  completed_at TEXT,
+  outcome TEXT CHECK(outcome IN ('success','failed','cancelled') OR outcome IS NULL),
+  notes TEXT,
+  FOREIGN KEY(project_id) REFERENCES projects(id) ON DELETE SET NULL,
+  CHECK ((status IN ('completed','failed','cancelled') AND completed_at IS NOT NULL AND outcome IS NOT NULL) OR (status NOT IN ('completed','failed','cancelled') AND completed_at IS NULL AND outcome IS NULL))
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_work_items_one_in_progress_per_agent
+ON work_items(assigned_agent)
+WHERE status = 'in_progress' AND assigned_agent IS NOT NULL;
+
+CREATE INDEX IF NOT EXISTS idx_work_items_status ON work_items(status);
+CREATE INDEX IF NOT EXISTS idx_work_items_agent_status ON work_items(assigned_agent, status);
+CREATE INDEX IF NOT EXISTS idx_work_items_project_id ON work_items(project_id);
+CREATE INDEX IF NOT EXISTS idx_work_items_created_at ON work_items(created_at);
+
+CREATE TABLE IF NOT EXISTS dispatch_log (
+  id TEXT PRIMARY KEY,
+  work_item_id TEXT NOT NULL,
+  dispatched_at TEXT NOT NULL,
+  agent TEXT NOT NULL,
+  completed_at TEXT,
+  outcome TEXT CHECK(outcome IN ('success','failed','cancelled') OR outcome IS NULL),
+  FOREIGN KEY(work_item_id) REFERENCES work_items(id) ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS idx_dispatch_log_work_item_id ON dispatch_log(work_item_id);