feat(mcp): add session tool profiles

[doyled-it]

Summary

Adds session-time MCP server/profile selection so new sessions can launch with a narrower MCP surface while preserving the default all-servers behavior.

Changes

• Adds persisted MCP selections and named MCP profiles to app config/session storage.
• Adds new-session controls for applying profiles and toggling runner-specific MCP servers.
• Enforces selected MCP access at runner launch/restart time, rejecting unsupported narrowed tool selections instead of silently widening access.
• Shows MCP profile/selection details in session metadata and documents the new controls.

Testing

• cargo fmt --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo build --release --all-features
• prek run --all-files
• Manually exercised the affected new-session MCP flow

Screenshots / Recordings

Not included. This is a TUI flow; the new-session MCP selector was manually exercised locally.

Version Label

version:minor

Related Issues

Closes: #66

Checklist

• Commits follow Conventional Commits
• Code follows the layering rules in CONTRIBUTING.md (no UI imports in core/, no state mutation in ui/)
• New code is covered by tests where practical
• Documentation (README, in-repo docs, help overlay) updated if behavior changed
• A version:* label is applied (or this change intentionally ships without a release)