ci(release): adopt the release/v* branch convention

[roncodes]

Adopts the release/v0.0.0 branch convention. Companion to fleetbase/fleetbase#641, which holds the reusable workflow this delegates to.

What changed

One line, so the caller matches either prefix:

if: github.event_name == 'workflow_dispatch' ||
    (github.event.pull_request.merged == true &&
     (startsWith(github.event.pull_request.head.ref, 'release/v') ||
      startsWith(github.event.pull_request.head.ref, 'dev-v')))

Why both, rather than a cutover

A hard switch would leave any release branch already open unrecognised — and a merge that produces no tag and no publish looks exactly like a successful one. dev-v* keeps working; drop that arm once no such branch remains open.

Merge order

fleetbase/fleetbase#641 first. This caller references the reusable workflow at @main, so release/v* only starts being accepted once that lands. Merging this one early is harmless — it just keeps behaving as it does today.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7f0ba99) to head (eb1f725).

Additional details and impacted files

@@             Coverage Diff             @@
##                main       #97   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity      1775      1775           
===========================================
  Files            135       135           
  Lines           7785      7785           
===========================================
  Hits            7785      7785           

Flag	Coverage Δ
backend	100.00% <ø> (ø)

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[roncodes]

Reviewed this against the live workflows — the change here is correct, but merging it alone won't enable the convention, and there was a conflict with the v0.4.21 release branch that I've now removed.

1. The real blocker is fleetbase/fleetbase#641, still open. The reusable workflow this delegates to at @main currently reads:

if [[ "$HEAD_REF" != dev-v* ]]; then
  echo "::error::Head branch '${HEAD_REF}' is not a dev-v* release branch."

So with this PR merged and #641 not, a release/v* merge passes this gate and is then refused by the reusable workflow. It fails loudly rather than silently, which is the better failure — but there's still no tag. Your merge-order note is right; it just needs #641 to actually land.

2. Conflict with #100, resolved on my side. The v0.4.21 release branch had briefly carried the same gate change, which conflicted with this PR (verified by test-merge: .github/workflows/release.yml). I've dropped it there so this PR owns the change — the two now merge clean in either order.

3. Nothing else in this repo assumes dev-v. Grepped the workflows: release.yml was the only functional reference. README.md:225 mentions dev-v0.4.19 in a coverage note, which is stale prose rather than a convention dependency.

Order to unblock the v0.4.21 release: fleetbase/fleetbase#641 → this → #99 and #98 into release/v0.4.21 → #100.