feat(app): session details menu in the header - #57528

Issue for this PR

N/A

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Consolidates the desktop session header actions into the session details menu.

• The ⋯ after the session title is removed. The Session details button uses the ⋯ icon instead and opens the details as a real Menu (the shared component the project / worktree menu uses), so it has the same gap, card, rows and keyboard behavior.
• The menu is one flat list: worktree (move submenu), changed files, Export…, Delete… (destructive color), then MCP, Plugins, Skills and LSP submenus. The collapsible project / extensions sections and their stored preferences are gone. The narrow-screen drawer is unchanged.
• The branch moves to the breadcrumb (project / worktree) menu, including "No branch · Based on …" for detached worktrees.
• MCP submenu: per-server switches are removed; status shows as text, and Sign in / Details stay. A new "Manage MCP servers" item opens the same dialog as /mcp.
• Export and Delete reach the app through a new extension host API, layout.command(id), which runs an app command like the palette. session.delete is a new command next to session.rename.
• The review toggle uses the same hover / pressed colors as the other header buttons.
• The header no longer stacks the breadcrumb onto a second row below 1000px; it stays one 48px row and truncates.

Rename stays on clicking the title and Ctrl+R.

How did you verify your code works?

• bun typecheck in packages/app and packages/gui-extensions; lint:changed clean.
• Ran the beta web app against a real server and exercised the header, the details menu, its submenus, Manage MCP servers, and window resizing in the browser.
• Header / session-summary e2e tests still assert the old layout and will be updated in follow-up commits on this PR.

Screenshots / recordings

Screenshots: https://jamesbox.exe.xyz/canvas/c/mSxZCqwqak

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR