ci: optimize build + deploy + migrate workflows (#51)

## Optimize CI/CD Workflows

### Changes

#### build.yaml
- **Merge 3 cargo steps → 1 compile pass**: `cargo build`, `cargo test`, `cargo clippy` now run in single invocation, reusing compiled artifacts
- **Remove `cargo clean`**: Eliminated wasteful step that deleted artifacts before Docker build
- **Add secret validation**: Registry credentials checked before login (fail-fast)

#### deploy.yaml
- **Skip checkout**: Removed unnecessary git clone
- **Fetch SHA via Gitea API**: Query latest commit directly instead of cloning
- **Reuse existing token**: Use `FORGEJO_REGISTRY_TOKEN` for Gitea API auth (already has privileges)
- **Validate image exists**: Check SHA image exists before tagging as latest (prevents tagging non-existent images)
- **Add secret validation**: Registry credentials checked before login (fail-fast)

#### migrate.yaml
- **Merge schema verification**: Schema inspect result reused in both changed + manual paths
- **Fix manual trigger errors**: Manual mode now fails on first migration error (was silently masking with `|| true`)
- **Track failures**: Explicit FAILED flag tracks migration errors across loop

### Benefits

- **Speed**: Fewer compiles, no unnecessary clones, reuse artifacts
- **Reliability**: Secret validation catches configuration issues early
- **Safety**: Image existence check prevents tagging phantom images
- **Clarity**: Merged steps have descriptive names, explicit error handling

### Testing

- Branch: `ci/optimize-workflows`
- Ready to merge to `main` after review

---------

Co-authored-by: rock <[email protected]>
Reviewed-on: #51
Co-authored-by: poimen <[email protected]>

k8s/app/kustomization.yaml

@@ -1,13 +1,11 @@
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 namespace: poimen
+
 resources:
-  # vault-pvc.yaml removed — memory service uses pgvector, not local storage
   - deployment.yaml
   - service.yaml
-  - config.yaml
-  # obsidian.yaml retired — reference docs now via memory graph
-  # Legacy secret managed separately
-  # - secrets.yaml
+  - config.yaml        # Production config (SOPS-encrypted)
+
 generators:
   - secret-generator.yaml