Create versioned releases from manual workflow runs

[zorenkonte]

Summary

Lets a release be published from the Actions tab without a local git checkout. Running Release APK by hand with a plain version such as 0.2.0 now creates the v0.2.0 tag on the current main and publishes a full release, instead of only a manual-<run> pre-release.

Changes

• Create versioned releases from manual workflow runs: the version step recognizes an x.y.z input, sets the tag to vx.y.z and marks the release as not a pre-release; any other input keeps the old manual-<run> pre-release behavior. target_commitish pins the created tag to the commit the run checked out.
• Document publishing a release from the Actions tab: README Releases section.

Testing

• Workflow file parses as YAML; the tag-push path is unchanged.
• The regex branch was checked by hand against 0.2.0 (match), 0.0.0-manual (no match) and v0.2.0 (no match, on purpose: enter the version without the v).

Checklist

• cd tv && ./gradlew testDebugUnitTest assembleDebug passes (no code change)
• cd client && npm run lint && npm run build passes (no client change)
• No comments added to source files
• README updated when behavior, the API or setup changed
• Each commit is one logical change and builds on its own