Add MCP servers (Gitea, K8s, Postgres, filesystem, git) to harness agents

Wire 5 MCP servers into Claude Code agents spawned by the harness:
- Gitea MCP for repo/issue/PR management on self-hosted Gitea
- Kubernetes MCP with read-only RBAC for cluster inspection
- Postgres MCP with read-only user for database queries
- Filesystem and Git MCP scoped to task worktrees

Generates .claude/settings.json in each worktree before agent spawn.
Gracefully skips for Codex/OpenCode runtimes (no MCP support).

Also fixes node-pty build failure by using local Node.js headers
instead of downloading from unofficial-builds.nodejs.org (ECONNRESET).

apps/harness/k8s/base/kustomization.yaml

@@ -3,6 +3,8 @@ kind: Kustomization
 resources:
   - deployment.yaml
   - service.yaml
+  - rbac.yaml
   - harness-claude-credentials-sealed.yaml
   - harness-opencode-credentials-sealed.yaml
   - harness-db-credentials-sealed.yaml
+  - harness-mcp-credentials-sealed.yaml