fix(control-plane,manifests): resolve MCP sidecar TLS and api-server proxy failures (#1546)

## Summary

- **MCP sidecar TLS fix**: The `ambient-mcp` sidecar container in runner
pods was missing the OpenShift `service-ca` volume mount and
`SSL_CERT_FILE` env var, causing `x509: certificate signed by unknown
authority` errors when calling `ambient-api-server` over HTTPS
(service-serving certs). Added both, matching the existing runner
container configuration.
- **Backend proxy fix**: The `ambient-api-server` reverse proxy plugin
defaults `BACKEND_URL` to `http://localhost:8080` when unset. Since the
backend runs in a separate pod (`backend-service:8080`), all proxied
requests (credentials, session listing) returned 502. Added
`BACKEND_URL` to the production env patch.

## Root Cause

These issues were exposed by the `ambient-control-plane` deployment fix
(env[15] `value`/`valueFrom` conflict on `CP_RUNTIME_NAMESPACE`). Once
the control-plane was redeployed with the correct manifest, the MCP
sidecar started being injected into runner pods, surfacing the missing
TLS config. The `BACKEND_URL` gap has existed since the api-server proxy
plugin was introduced but was previously masked.

## Test plan

- [ ] Deploy updated `ambient-control-plane` image to cluster
- [ ] Create a new session and verify MCP tools (`list_sessions`,
`list_projects`) work without TLS errors
- [ ] Verify credential fetching (github, gitlab, etc.) returns proper
responses instead of 502
- [ ] Verify `acp_list_sessions` works without 502

🤖 Generated with [Claude Code](https://claude.ai/code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Enhanced MCP sidecar container configuration to support TLS
certificate validation and CA bundle access for secure internal
communication.
* Configured the API server with backend service endpoint URL settings
for production deployments, enabling proper service-to-service
connectivity in the ambient control plane.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: user <u@example.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: 4 people

components/ambient-control-plane/internal/reconciler/kube_reconciler.go

@@ -840,6 +840,7 @@ func (r *SimpleKubeReconciler) buildMCPSidecar(sessionID string) interface{} {
 		envVar("AMBIENT_CP_TOKEN_URL", r.cfg.CPTokenURL),
 		envVar("AMBIENT_CP_TOKEN_PUBLIC_KEY", r.cfg.CPTokenPublicKey),
 		envVar("SESSION_ID", sessionID),
+		envVar("SSL_CERT_FILE", "/etc/pki/ca-trust/extracted/pem/service-ca.crt"),
 	}
 	if r.cfg.HTTPProxy != "" {
 		env = append(env, envVar("HTTP_PROXY", r.cfg.HTTPProxy))
@@ -862,6 +863,14 @@ func (r *SimpleKubeReconciler) buildMCPSidecar(sessionID string) interface{} {
 			},
 		},
 		"env": env,
+		"volumeMounts": []interface{}{
+			map[string]interface{}{
+				"name":      "service-ca",
+				"mountPath": "/etc/pki/ca-trust/extracted/pem/service-ca.crt",
+				"subPath":   "service-ca.crt",
+				"readOnly":  true,
+			},
+		},
 		"resources": map[string]interface{}{
 			"requests": map[string]interface{}{
 				"cpu":    "100m",

components/manifests/overlays/production/ambient-api-server-env-patch.yaml

@@ -10,3 +10,5 @@ spec:
           env:
             - name: AMBIENT_ENV
               value: production
+            - name: BACKEND_URL
+              value: "http://backend-service.ambient-code.svc:8080"