chore: sync fork with upstream main

[Olivier-OG]

Problem

The fork's main had drifted 251 commits behind pingdotgg/t3code (up to the
v0.0.39 nightlies), so none of the recent upstream work was available here and
the gap was only going to get more expensive to close.

What this does

Merges upstream/main into the fork. Three conflicts came up, all of them two
sides adding different things in the same place, so all three keep both intents
— no upstream behaviour was dropped and nothing new was invented.

ProviderCommandReactor.test.ts — the "generates a worktree branch name
for the first turn" test. Our fix(server): drop the t3code/ prefix from generated branch names asserted the rename target no longer re-attaches
t3code/; upstream's feat(web): cite assistant responses with inline citations (pingdotgg#9146) asserted the persisted user message keeps the raw prompt,
citation markup included. Independent assertions, both kept. Checked against the
merged reactor that our buildGeneratedWorktreeBranchName change survived and
the call site still passes oldBranch/newBranch, so the prefix assertion
still exercises the fix rather than passing vacuously.

DesktopClientSettings.test.ts — the client settings fixture gained
panelAnimationDurationMs upstream and the notify* keys from #3 on main.
The fixture has to cover every schema key, so both groups stay.

SettingsPanels.tsx — #3 inserted <NotificationSettings /> ahead of the
About section; upstream gave that section id="about" so settings search can
target it. Kept the new panel and upstream's id.

A second merge commit brings in main (PR #3, native notifications), which
landed while this sync was in flight, so the branch is current with its base.

Verification

Scoped to the packages the resolutions touch, per AGENTS.md ("do not run
repo-wide checks" — CI owns the full suite):

• typecheck on apps/server, apps/desktop, apps/web — all exit 0. The
  server's 33 diagnostics are pre-existing Effect style suggestions, none in a
  touched file.
• ProviderCommandReactor.test.ts — 61/61 pass.
• DesktopClientSettings.test.ts — 7/7 pass.
• settingsSearch, settingsLayout, SettingsPanels.logic — 44/44 pass.
• vp fmt --check and vp lint clean on all three files; the remaining
  warnings are pre-existing and hundreds of lines from the resolutions.

No UI change originates here, so there are no before/after images to attach —
the web diff is upstream's own work plus a two-line reconciliation.

Caveats

I deliberately did not run the repo-wide test suite, so upstream regressions
outside apps/server, apps/desktop and apps/web are unverified locally and
left to CI.

<NotificationSettings /> renders its own sections without an id, so the new
notification settings are not reachable from settings search the way the
neighbouring sections now are. That is pre-existing from #3 rather than
something this merge changed, and adding ids felt like inventing behaviour in a
conflict resolution — worth a follow-up.

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Claude Opus 5 (1M context) via Claude Code, driven from T3 Code.