redesign channels: single-column sidebar + full-width title bar

[adamleithp]

Summary

Redesign of the Channels space UI — moves from a two-column layout (app rail + 260px channel pane) to a single self-contained sidebar under a full-width title bar.

Possible nits you may have

• that bar at the top is so empty!... yes, but that's room for search/help button...
• Another window in a window design? Meh, yea for now. It's all just temporary anyways.
• How do i get back to "Code"? Just hit home at the top or any other main nav items, they're not ported over and just reroute to the other

Layout

• New ChannelsSidebar: one 220px column owning the left pane — workspace switcher (top), global nav, channel tree, Settings (pinned bottom). No app rail in this space.
• __root.tsx Channels-space layout reworked into a vertical shell with a full-width title bar carrying the PostHog mark (left-padded to clear the macOS stoplights). Drops the old AppNav + bordered 260px column.
• Global nav (Home / Global Inbox / Agents / Files) folded into the sidebar as SidebarItem rows via ChannelsNav.

Project switcher

• ProjectSwitcher gains a compact button trigger variant (project name + chevron) for the Channels header, alongside the existing item variant used in the Code sidebar.
• Menu width is now per-variant: button pins a fixed w-64 (the full-width trigger would otherwise stretch the menu via --anchor-width and break its layout); item still matches its anchor.

Dashboards / data

• DashboardsService.list now filters a single listAll() by meta.channelId instead of a per-channel server-side parent query, simplifying the path.
• Removes now-unused fields from domain-types and the posthog-client.

Test

• pnpm --filter @posthog/ui typecheck clean.
• Lint + typecheck pass via pre-commit hooks.

🤖 Generated with Claude Code

[greptile-apps]

Comments Outside Diff (1)

1. packages/ui/src/styles/globals.css, line 1879-1881 (link)

   Global hover rule affects all outline buttons

   This rule targets every .quill-button--variant-outline element app-wide, not just the ProjectSwitcher trigger. Any existing outline button that had a different hover treatment (or intentionally no hover background) will silently pick up var(--color-fill-hover) after this change. The side-effect is invisible in the PR diff but could produce visual regressions across unrelated surfaces.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: packages/ui/src/styles/globals.css
   Line: 1879-1881
   
   Comment:
   **Global hover rule affects all outline buttons**
   
   This rule targets every `.quill-button--variant-outline` element app-wide, not just the `ProjectSwitcher` trigger. Any existing outline button that had a different hover treatment (or intentionally no hover background) will silently pick up `var(--color-fill-hover)` after this change. The side-effect is invisible in the PR diff but could produce visual regressions across unrelated surfaces.
   
   How can I resolve this? If you propose a fix, please make it concise.

   Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
packages/ui/src/styles/globals.css:1879-1881
**Global hover rule affects all outline buttons**

This rule targets every `.quill-button--variant-outline` element app-wide, not just the `ProjectSwitcher` trigger. Any existing outline button that had a different hover treatment (or intentionally no hover background) will silently pick up `var(--color-fill-hover)` after this change. The side-effect is invisible in the PR diff but could produce visual regressions across unrelated surfaces.

_{Reviews (1): Last reviewed commit: "fix(channels): pin project switcher menu..." | Re-trigger Greptile}

[stamphog]

Review agent failed — check the workflow run and re-apply the label to retry.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 3754929.}

[stamphog]

This is a pure UI redesign with no logic, security, or data model changes, but at 711 lines it exceeds the auto-approval size ceiling and has zero reviews — request a teammate review before merging.

[raquelmsmith]

This looks great. Two things: https://www.loom.com/share/95b33022b38c469480ccbfc2a9836289