Add All Projects channel view

[iamnbutler]

Closes #145.

• Add All Projects at the top of the shared project selector; choosing it opens Channels.
• Group the ten most recently active, non-archived channels from each project under collapsible project-name sections. Retain the grouped view when opening channels.
• Keep concrete project selection for channel creation and GitHub views, and apply local/remote permissions per channel.

Validation:

• bun types, bun run ci, and bun app build pass.
• Signed native dev build succeeded. Its process crashed immediately after launch, tracked separately in Ace-dev crashes shortly after launch with SIGTRAP in bundled Bun worker #150; native interaction remains unverified.
• Smoke-checked the same source-host app in Safari using Ace desktop tools with 13 real channels across two projects: ten-channel cap, archived exclusion, live activity reordering, channel selection preserving All Projects, section collapse, Dashboard retaining the selected concrete project, and All Projects/selected channel restored on reload.

Built in Ace

Built entirely in Ace using its lane, file, shell, subagent review, and desktop tools. Safari displayed the local app for smoke verification because the native dev process crashed (#150); Chrome observation also hit existing githubnext/desktop-tools#6. No external editor or terminal was used.