fix(mcp-config-validator): remove invented trust field (verify-first)

`.mcp.json` has no per-server `trust` key — verified 2026-06-18 against
code.claude.com/docs/en/mcp + /settings. MCP server approval is
dialog/settings-based (enableAllProjectMcpServers / enabledMcpjsonServers /
disabledMcpjsonServers), never a JSON field. The scanner's "Missing trust
level" (CA-MCP-001, medium) and "Invalid trust level" (high) were false
positives flagging a field that does not exist.

- scanner: delete both trust checks + VALID_TRUST_LEVELS; drop `trust` from
  VALID_SERVER_FIELDS so a stray `trust` is now flagged as an unknown field
- humanizer: remove the two trust-level entries
- knowledge (5 files): point to the real approval mechanism, not a trust field
- fixtures: scrub `trust` (incl. the invalid "local" in optimal-setup)
- tests: flip assertions (no trust-level finding; stray trust -> unknown
  field) + add knowledge-staleness re-freeze guards
- snapshots: reseed (marketplace-medium .mcp.json -8 tokens, hermetic)
- gap-matrix: mark the trust verify-first item DONE

Suite: 853/853 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8

knowledge/configuration-best-practices.md

@@ -56,7 +56,7 @@
 
 1. **Commit `.mcp.json` to git.** Team-shared MCP servers belong in `.mcp.json` at project root, not in individual `~/.claude.json` files. One commit, everyone gets the servers.
 2. **Set `enableAllProjectMcpServers: true` in project settings.json** for zero-friction team onboarding. New team members don't have to manually approve each server.
-3. **Set trust levels explicitly.** `"trust": "workspace"` for project-specific servers; `"trust": "trusted"` only for servers you fully control. Default is untrusted (sandboxed).
+3. **Approve servers via settings, not a `trust` field.** `.mcp.json` has no per-server `trust` key — approval is recorded by the workspace-trust and MCP-approval dialogs. For non-interactive, granular control set `enabledMcpjsonServers: ["memory", "github"]` / `disabledMcpjsonServers: [...]` in settings.json instead of approving each server by hand.
 4. **Use `@server:resource/path` for dynamic data.** `@github:repos/owner/repo/issues` pulls live data into context. More reliable than asking Claude to fetch and parse.
 5. **Deny MCP tools you don't want Claude to invoke.** `{"permissions": {"deny": ["mcp__filesystem__write_file"]}}` — even with a server connected, specific tools can be blocked.