Give each tracked package its own PR, and let a fresh branch tip fall back

The branch tracker stalled omarchy-dev and omarchy-settings-dev twice in a
week:

- All ~50 auto_merge packages rode one PR, so omasnap-git's failing smoke
  suite kept the quattro pins unmerged from Oct 4 to Oct 8 (#788). Each
  package now gets its own PR on auto/track-branches-<package>; packages
  pinned from the same branch share one, since they move in lockstep. A run
  closes tracker PRs that master has moved past, and the old single PR.
- A branch tip younger than min_release_age held the whole branch, so a
  run that landed shortly after a quattro commit pinned nothing. The watch
  now falls back along first-parent history to the newest commit that has
  cleared the window, measured from clone time so siblings agree.
- The every-2-hours schedule fired every 6 to 9 hours in practice; run it
  hourly.

docs/upstream-sources.md

@@ -73,13 +73,17 @@ because its published history counted every commit and the number must never
 go down.
 
 `min_release_age` holds a branch tip until its commit timestamp is old enough.
-A fresh tip leaves the existing pin alone; the watch never walks backward to
-an older commit. This uses Git's committer date, not the time a commit was
-pushed. `BYPASS_MIN_RELEASE_AGE=1` bypasses the hold.
+A fresh tip falls back to the newest commit on the branch's first-parent
+history that has cleared the window, so a busy branch still advances; it never
+selects a commit from a merged side branch. This uses Git's committer date, not
+the time a commit was pushed, measured from when the run cloned the branch so
+packages pinned from it agree. `BYPASS_MIN_RELEASE_AGE=1` bypasses the hold.
 
 Packages marked `"auto_merge": true` ride the unattended lane
 (`track-branches.yml`) instead of the reviewed sync PR: their bump PR is opened
-and auto-merged as soon as the build checks pass. The lane works with every
+and auto-merged as soon as the build checks pass. Each package gets its own
+PR on `auto/track-branches-<package>`, and packages that pin the same branch
+share one, so a package whose build fails holds back only itself. The lane works with every
 provider, not only branch watches, so it also carries release feeds trusted to
 ship without review: the browsers, large vendors' apps, Omacom's own projects,
 and vendor binaries that hold fresh releases with `min_release_age`. `bin/sync-upstream --lane
@@ -229,8 +233,8 @@ These packages were already excluded from automatic AUR updates. The migration p
 `sync-upstream.yml` pushes its PR with the built-in `GITHUB_TOKEN`, so GitHub
 holds the PR's build and test runs for approval. The workflow labels its own
 PR `build-approved`, and its `approve` job releases the held runs for each
-commit it pushes. A push to an `auto/sync-*` branch, or to the tracker's
-`auto/track-branches`, does not cancel the PR's build in flight: the new
+commit it pushes. A push to an `auto/sync-*` branch, or to one of the
+tracker's `auto/track-branches-*` branches, does not cancel the PR's build in flight: the new
 build waits, then reuses every artifact the finished one uploaded.
 
 Because of that push, GitHub starts no `pull_request_target` workflow for the