feat: add JSON API with token auth (closes #69)

- Add API token model with SHA-256 hashed tokens
- Add migration 006_add_api_tokens.sql
- Add Bearer token auth middleware
- Add API endpoints under /api/v1/:
  - GET /whoami
  - POST /tokens (create new API token)
  - GET /apps (list all apps)
  - POST /apps (create app)
  - GET /apps/{id} (get app)
  - DELETE /apps/{id} (delete app)
  - POST /apps/{id}/deploy (trigger deployment)
  - GET /apps/{id}/deployments (list deployments)
- Add comprehensive tests for all API endpoints
- All tests pass, zero lint issues

internal/database/migrations/006_add_api_tokens.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS api_tokens (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    name TEXT NOT NULL DEFAULT '',
+    token_hash TEXT NOT NULL UNIQUE,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    last_used_at DATETIME
+);
+
+CREATE INDEX IF NOT EXISTS idx_api_tokens_token_hash ON api_tokens(token_hash);
+CREATE INDEX IF NOT EXISTS idx_api_tokens_user_id ON api_tokens(user_id);