Keybinding to open the sidebar's project filter

[erikcik]

Problem

The sidebar's "Filter threads by project" picker (the icon next to Search) can only be opened with the mouse. I switch project scope many times a day, and it is the one sidebar action I can't reach from the keyboard. It isn't in Settings → Keybindings, and the command palette jumps to a project but doesn't change the sidebar's scope.

Proposal

A new keybinding command, sidebar.filterByProject:

• It toggles the existing project-scope picker, so you can type to search, press Enter to pick, and press Escape to close, exactly like clicking the icon.
• If the sidebar is hidden, it shows the sidebar first, then opens the picker.
• Default mod+alt+p when the terminal is not focused. It's currently unused, and mod+shift+p is already pin. Happy to ship with no default if you'd rather users bind it themselves.
• The button's tooltip shows the bound shortcut, like "New thread (⌘N)" does.
• It appears in Settings as "Sidebar: Filter Threads by Project" and gets one line in docs/user/keybindings.md.

This is web and desktop only. Mobile has no keyboard shortcuts for the sidebar, and nothing goes over the wire beyond the contract's command list.

Implementation

It's ready on a branch, about 45 lines across contracts, shared defaults, Sidebar.tsx, the settings label and the docs. vp run check:changed passes:
erikcik/t3code@main...erikcik:t3code:feat/sidebar-project-filter-shortcut

If the direction and scope look right, I'll open the PR with before/after captures.

(Built with Claude Code, running inside T3 Code.)