ci: make a release a shipment rather than a merge

release.yml fired on every push to main, so the trigger was "a PR was
merged" and nothing else decided. That is a version per unit of *work*
rather than per *shipment*: eight releases in twenty-two hours, v0.0.1
through v0.3.1, for one session -- each fanning out to four publishers on
a runner with capacity 1, so roughly forty packaging jobs shipped three
issues while ordinary PR CI queued behind them. pacman, Homebrew and
Obtainium see every one.

The push trigger is gone and workflow_dispatch, which was already there
and already worked, is the whole mechanism. Nothing else had to change to
batch releases, because semantic-release already reads every commit since
the last tag: five fixes and two feats become one minor release with all
seven in the notes. Release frequency was only ever how often this file
fired.

This is the rule index-artifact.yml states and is the other instance of:
a job that mutates state which cannot be rebuilt in ten minutes is
triggered deliberately, not by a push. A release here is a tag, a Gitea
release, an Arch package, a Homebrew formula, a signed APK and desktop
assets -- and an Android version going backwards costs the user their
library.

`dry_run` is what makes a manual trigger usable: the point of pulling a
lever by hand is being able to look first, so the input runs
semantic-release --dry-run -- the version and the notes, no tag, no
release, no publishers. Anything but the literal string "true" releases
for real, because a typo in a dispatch box must not silently turn a
shipment into a green no-op.

Two alternatives were considered and rejected, both recorded on the
issue. A `beta` integration branch relocates the trigger rather than
removing one: it needs a second protected branch carrying the same
required checks, and it *adds* a full check + e2e run per batch on the
very runner whose queue is the complaint. A schedule batches without
anyone having to remember, but puts the decision back on a timer, which
is the thing being removed.

Closes #115

.releaserc.yml

@@ -1,8 +1,19 @@
 # semantic-release configuration.
 #
-# Runs on pushes to main from .gitea/workflows/release.yml: determine the
-# version from the Conventional Commits since the last tag, write the
-# changelog, commit it, push the tag, and create the Gitea release.
+# Run by hand from .gitea/workflows/release.yml, which has no push
+# trigger: determine the version from the Conventional Commits since the
+# last tag, write the changelog, push the tag, and create the Gitea
+# release.  A release is a shipment rather than a merge, and the commits
+# accumulate until someone says so -- this file needs to know nothing
+# about that, because reading everything since the last tag is what it
+# already did.
+#
+# `branches` is main and only main.  A `prerelease: true` channel is the
+# obvious next edit here and is the one to think twice about: all four
+# publishing workflows trigger on `v*`, which matches `v0.4.0-beta.1`.
+# They carry a prerelease guard now, so the failure is a clean skip
+# rather than a beta in a public tap -- but they are four separate files
+# and this is the line that would turn them on.
 #
 # **There is no `@semantic-release/github` plugin here and there must not
 # be.** Gitea's API is `/api/v1` and is not GitHub's surface. The Gitea