[Feature]: Expose MCP permissions and project context policy in Settings

[Dencyuman]

Use case

MCP on Desktop has substantial configuration requirements beyond the current on/off connections panel, and no surface exposes them. Per docs/ai-integration.md and the access/agent-scope model, configuration spans three levels:

1. Connections (exists, minimal): local transport enable, connection lifecycle, restart.
2. Permissions / agent scopes (missing): per-agent scopes (read / propose / apply), capability grants (graph:write, schema:write, view:write …), proposal-only vs direct-apply policy, session expiry. Today these values exist in the backend and even leak raw session IDs into the hub UI, but nothing lets the user set them.
3. Project-dependent context policy (missing): what context an AI client may fetch from this project — bounded subgraph limits, token budgets, search capabilities exposure, redaction. These are project-level decisions and belong with the project, not global app settings.

Suggested shape

• A Settings surface with an MCP section covering app-level defaults (transport, default scope policy) and a per-project section covering agent scopes and context policy.
• Scope and grant edits flow through the existing access/agent-scope enforcement (internal/access), not a parallel store.
• Mock-first: design the Settings screen (including Language, and MCP sections) with owner review before implementation, consistent with the hub/workspace mock vocabulary.

Acceptance criteria

• Users can view and edit agent scopes and apply-policy per connection without touching config files.
• Project-level context policy (bounded fetch limits, token budget, capability exposure) is editable and persisted with the project.
• No raw session identifiers in primary UI; sessions shown with human-readable state and expiry.
• All strings via the i18n catalog (en/ja).

Constraints

• Enforcement stays in Go access components; UI is presentation over existing decisions (architecture.md).

Dependency

Depends on the shell rebuild (#172) for the Settings surface. Related: #157 (connections backend), #158 (review workflow).