fix(installer): automate custom MCP providers and keyed headers

[LinoyBitan1]

Summary

Allow a SAW-BOM to configure custom MCP providers automatically, so a sandbox can use a named in-cluster MCP Service through Option A without manual provider creation and attachment. Support both no-key and API-key authentication.

JIRA: APPENG-6573

Changes

• Accept custom governance profiles using credentialFree: true or credentialEnv with credentialSecret. Validate them against the gateway's live profile catalog, skip transient missing profiles without pruning, and keep MCP/search providers separate from inference providers.
• Configure native MCP headers for OpenClaw 2026.9.6, whose bundle HTTP client passes ${VAR} header strings literally. Store only placeholders inside the sandbox; the real key stays with OpenShell. Native entries override same-name bundle defaults; retain mcp.json for the bundle's mcpServers capability.
• Track managed native entries in the existing ledger, remove obsolete entries and credentials, and preserve unrelated manual MCP configuration. Validate credential key names before cleanup.
• Give catalog read failures an actionable governance diagnostic. Defer failed native config reads to verification and accumulate native drift alongside bundle/plugin failures.
• Document the governance profile, BOM, bundle and Secret configuration, including host, port, binary and negotiated MCP-version checks for 403 policy_denied.
• Add installer regression tests. The change does not deploy an MCP Service or enable a concrete profile by default.

Validation

• All 491 installer tests validated: the restricted full run passed 477 and hit 14 loopback-socket permission failures; all 92 tests in the affected modules passed when rerun with socket access. Nine new review regression cases passed before the full run. git diff --check passed.
• Fresh Argo deployment into a new VM and sandbox succeeded without manual provider creation, attachment or native-header configuration.
• Real agent discovery and tool calls succeeded for in-cluster no-key, in-cluster keyed, optional-key and external DeepWiki MCP servers. All four runs had zero tool failures.
• The keyed server confirmed authorization. The sandbox credential comparison confirmed it received a placeholder rather than the real Kubernetes Secret value.
• An Argo update from optional-key to credential-free mode automatically cleared the stored credential and obsolete native override.
• Review fixes have local regression coverage; the live Argo scenarios above were run before this review update.

Separate gateway lifecycle follow-up

The first agent call after the live update timed out because OpenClaw's gateway restart encountered StateDatabaseCoordinatorContentionError: another OpenClaw process owns gateway-lifecycle. The installer reported Done while the gateway was unavailable. Fresh-install validation passed; post-update agent validation failed.

The restart function is unchanged from this PR's base commit fc385020014e51f1341b49a6bfe3819c3e09d246 (Python AST comparison). This pre-existing gateway lifecycle and success-reporting defect is tracked separately in #94 and does not block the custom MCP changes in this PR.