feat: load profiles.json v2 contexts shape with enabled enforcement and LLM-safe output (#120)

Support the canonical contexts-shape version 2 config (contexts / profiles /
projects / rules) alongside the existing environments shape and v1:

- Require a boolean 'enabled' on every context, profile, service, and
  project. Disabled entries are surfaced in audits but fail closed at
  selection/resolution — never a silent fallback to another profile,
  service, or credential source.
- Resolve the active identity from GITEA_MCP_PROFILE via the existing
  select_profile path; profile base_url falls back to the context's enabled
  gitea block.
- Add resolve_service() and project_for_path() for context service and
  project-to-context resolution (internal use; fail closed on disabled).
- get_auth_header now propagates ConfigError when GITEA_MCP_CONFIG is set
  instead of silently degrading to Basic auth.
- Hide endpoint URLs and keychain ids from normal LLM-facing output:
  gitea_whoami / gitea_get_profile report logical names and auth status
  only; new gitea_audit_config tool reports enabled/disabled state and safe
  one-line service summaries. The GITEA_MCP_REVEAL_ENDPOINTS opt-in (and
  'python3 gitea_config.py audit --reveal-endpoints' locally) restores
  endpoints and auth source names for admin diagnostics; token values are
  never printed on any path.
- Ship gitea-mcp.v2-contexts.example.json (synthetic values) and validate
  it in tests.

Implements #120

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -6,6 +6,7 @@ __pycache__/
 # Real JSON runtime-profile configs may reference private hosts; keep only the example.
 gitea-mcp*.json
 !gitea-mcp.example.json
+!gitea-mcp.v2-contexts.example.json
 .vscode/
 graphify-out/
 branches/