feat(docker-watcher): phase 7 - deployer & health checker

Deploy orchestrator with full pipeline: pull → create container →
start → network → NPM proxy → health check. Rollback on failure,
multi-instance support, max_instances enforcement, webhook notifications.
Fix NPM auth in rollback and error logging in removeInstance.

plans/docker-watcher-core/phase-7-deployer.md

@@ -1,6 +1,6 @@
 # Phase 7: Deployer & Health Checker
 
-**Status:** ⬜ Not Started
+**Status:** ✅ Complete
 **Parent plan:** [PLAN.md](./PLAN.md)
 **Domain:** backend
 
@@ -9,17 +9,17 @@ Implement the core deployment orchestrator: pull → start container → configu
 
 ## Tasks
 
-- [ ] Task 1: Define deployer service struct — depends on Docker client, NPM client, store, notifier
-- [ ] Task 2: Implement deploy flow: pull image → create container → start → connect to network → configure proxy → health check
-- [ ] Task 3: Implement subdomain generation per convention: `stage-{stage}-{project}` for default, `stage-{stage}-{project}-{tag}` for specific
-- [ ] Task 4: Sanitize tags for DNS (dots → dashes, lowercase, truncate)
-- [ ] Task 5: Implement health checker — HTTP GET to `http://container:{port}{healthcheck_path}` with retries and timeout
-- [ ] Task 6: Implement rollback on health check failure — remove new container, delete NPM proxy host, update instance status
-- [ ] Task 7: Implement multi-instance support — multiple tags of same project/stage can run simultaneously
-- [ ] Task 8: Implement max_instances enforcement — remove oldest instance when limit reached
-- [ ] Task 9: Implement notification webhook — POST to configured URL on deploy success/failure
-- [ ] Task 10: Create deploy history records in store (status, timestamps, logs)
-- [ ] Task 11: Implement deploy log streaming — append log entries during deploy for real-time visibility
+- [x] Task 1: Define deployer service struct — depends on Docker client, NPM client, store, notifier
+- [x] Task 2: Implement deploy flow: pull image → create container → start → connect to network → configure proxy → health check
+- [x] Task 3: Implement subdomain generation per convention: `stage-{stage}-{project}` for default, `stage-{stage}-{project}-{tag}` for specific
+- [x] Task 4: Sanitize tags for DNS (dots → dashes, lowercase, truncate)
+- [x] Task 5: Implement health checker — HTTP GET to `http://container:{port}{healthcheck_path}` with retries and timeout
+- [x] Task 6: Implement rollback on health check failure — remove new container, delete NPM proxy host, update instance status
+- [x] Task 7: Implement multi-instance support — multiple tags of same project/stage can run simultaneously
+- [x] Task 8: Implement max_instances enforcement — remove oldest instance when limit reached
+- [x] Task 9: Implement notification webhook — POST to configured URL on deploy success/failure
+- [x] Task 10: Create deploy history records in store (status, timestamps, logs)
+- [x] Task 11: Implement deploy log streaming — append log entries during deploy for real-time visibility
 
 ## Files to Modify/Create
 - `internal/deployer/deployer.go` — main deploy orchestrator