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/deployment.yaml

@@ -14,6 +14,7 @@ spec:
       labels:
         app: harness
     spec:
+      serviceAccountName: harness
       imagePullSecrets:
         - name: gitea-pull-secret
       containers:
@@ -33,6 +34,18 @@ spec:
                 secretKeyRef:
                   name: harness-db-credentials
                   key: database-url
+            - name: GITEA_TOKEN
+              valueFrom:
+                secretKeyRef:
+                  name: harness-mcp-credentials
+                  key: gitea-token
+            - name: GITEA_URL
+              value: "http://gitea.platform.svc:3000"
+            - name: HARNESS_PG_MCP_URL
+              valueFrom:
+                secretKeyRef:
+                  name: harness-mcp-credentials
+                  key: postgres-mcp-url
           volumeMounts:
             - name: workspace
               mountPath: /data/harness