feat(mcp): add profile management

[doyled-it]

Summary

Adds in-app MCP profile management so users can create and maintain reusable MCP selections without editing config. Also wires profile save/update actions into New Session while preserving the final per-session MCP snapshot.

Changes

• Add the Manage MCP Profiles command palette action and modal for creating, editing/renaming, duplicating, and deleting MCP profiles.
• Add New Session Ctrl+P and Ctrl+U profile actions, plus README/help overlay documentation.
• Keep missing or renamed profile servers visible during editing and ignore missing enabled servers at runner launch instead of blocking session creation.

Testing

• cargo fmt --check via prek run --all-files
• cargo clippy --all-targets --all-features -- -D warnings via prek run --all-files
• cargo test --all-features via prek run --all-files
• cargo build --release --all-features via prek run --all-files
• Manually exercised the affected flows with target/release/agent-view under a temporary HOME, opening Manage MCP Profiles from the command palette and rendering the profile list/create editor.

Screenshots / Recordings

N/A.

Version Label

version:minor

Related Issues

Closes: #70

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)