fix(release): restore beta release creation

[tulayha]

Summary

• restore Release Please's standard grouped pull-request titles
• make the unprefixed core release participate correctly in linked versioning
• reconcile the partially bumped 0.4.0-b desktop and release manifests
• add packaging coverage for the linked-version configuration

Root cause

The core package deliberately omits its component from tags, so Release Please exposes its plugin component as an empty string. The linked-version configuration instead named it vidxp. Preconfiguration therefore skipped the core component, while post-processing still grouped its lone candidate onto a componentless release branch. After PR #38 merged, Release Please rejected that branch/component combination and returned release_created=false, so the TestPyPI workflow was skipped.

The custom grouped PR title also obscured the release metadata and emitted parser warnings, so this restores Release Please's native title handling.

Validation

• python -m unittest tests.test_packaging -v
• ruff check tests/test_packaging.py
• git diff --check