feat(desktop): Projects follow-ups — access restrictions, fast loading, activity feed polish

[thomaspblock]

Summary

Follow-up batch on the Projects overview (continues merged #1677):

• Repository access restrictions — repositories the viewer can't reach are surfaced with a reason instead of failing silently. Channel-ACL denials (which arrive as the same 404 as a missing repo, for anti-enumeration) are re-classified using the repository's channel binding and the viewer's memberships (useRepositoryAccess.ts, projectRepoAvailability.ts).
• Projects loads in seconds instead of minutes — enumeration no longer crawls every kind:5 deletion event on the relay. It fetches project/repo announcements first, then queries deletions scoped to those coordinates via chunked #a filters (3 queries instead of hundreds on staging).
• Activity feed layout polish — bare event-type glyph beside the headline (no badge circle), timeline spine runs through the avatars connecting consecutive cards, linkable actor/project names are bold in theme foreground, rounded hover state, alignment fixes.
• Create button pinned — the "+" create menu is pinned to the pane's top-right corner (equal 16px insets) and no longer scrolls away with the page header.
• List controls as a table header — the scope selector (left) and sort + layout toggle (right) render as the first row of the list container on the Projects/Repositories/PRs/Issues tabs; in card view the identical bar stands alone with the cards below (ProjectsListHeaderBar.tsx).
• Repository rows show the git location — subtitle is github.com/org/repo for external repos or owner/repo (resolved profile name) for Buzz-hosted ones, instead of repeating the project name (repositoryDisplayPath).
• Uniform work-item row heights — issue rows previously ran the author chip in inline flow, letting the 20px avatar grow the line box ~3px taller than PR rows; both lists now share the same flex subtitle.

📸 Screenshots: feed layout / pinned button · list header / repo subtitles / row heights.

Note: two empty chore: retrigger CI commits exist on the branch from working around the Aug 6 GitHub Actions incident; happy to drop them with a signoff rebase before undrafting if preferred. Latest main is merged in (a0cc35220).

Test plan

• Desktop unit tests (4,493 pass after merging main), Biome, tsc
• New unit tests for scoped deletion enumeration and repo availability re-classification
• New unit tests for repositoryDisplayPath (external, Buzz-hosted, unresolvable)
• Screenshot verification of feed layout, connector spine, and pinned button (top + scrolled states) — posted to the PR
• Screenshot verification of the list header row (list + card), repo subtitles, and matching PR/issue row heights — posted to the PR
• Manual pass against staging (projects list load time, restricted-repo states)

[thomaspblock]

Screenshots of the UI changes in this PR (mock-bridge E2E build, light theme).

Activity feed layout

Bare event-type glyph beside the headline (no badge circle), the timeline spine runs through the avatars connecting consecutive cards, and the linkable actor/project names are bold in theme foreground while the rest of the meta line stays muted.

Create button pinned — top of page

The "+" create menu sits in the pane's top-right corner with equal 16px insets from the top and right edges.

Create button pinned — scrolled

After scrolling, the page header is gone and the tab bar is stuck to the top, but the create button hasn't moved — it's an overlay on the non-scrolling pane, not a sticky element.

[thomaspblock]

🤖 Screenshots for the list header / repository subtitle batch (dd6d0567a).

List view: controls are the table's first row

The scope selector (left) and sort + layout toggle (right) now render as a header row inside the list container — one shared border, divider below, subtle background tint.

Card view: same bar, same proportions

In the card layout the identical bar stands alone (fully rounded) with the cards flowing below.

Repository rows show where the git data lives

Instead of repeating the (often identical) project name, the subtitle is now github.com/org/repo for external repos or owner/repo (resolved profile name) for Buzz-hosted ones.

PR and issue rows share an identical height

Issue subtitles previously used inline flow, letting the 20px author avatar grow the line box ~3px taller than PR rows. Both now use the same flex subtitle.

[klopez4212]

Reviewed commit dd6d056 (Projects list controls/header redesign). I found no actionable correctness or blocking issues.

Validation: TypeScript typecheck, full unit suite (4,497 passed), desktop production build, local file-size/px-text/pubkey-truncation checks, and all GitHub CI checks passed. Local Playwright execution was unavailable because the build artifact/browser setup was not present; the GitHub Desktop smoke/integration E2E checks passed.