Correct stale release and Swift build documentation

Problem

Public documentation describes tag-triggered/manual-tag releases even though the workflow is manual-dispatch-only and creates tags itself. It also documents the wrong DMG filename and contradicts itself about whether swift test needs the vendored libghostty archive.

Evidence:

• https://github.com/richardcase/clowder/blob/b5492d5/README.md#L123-L161
• https://github.com/richardcase/clowder/blob/b5492d5/docs/code-signing.md#L143-L153
• https://github.com/richardcase/clowder/blob/b5492d5/docs/homebrew.md#L36-L50
• https://github.com/richardcase/clowder/blob/b5492d5/AGENTS.md#L48-L58 and #L191-L195

Acceptance criteria

• Make docs/versioning.md the canonical release procedure.
• Correct DMG names and dispatch instructions.
• Document archive-free Swift target builds separately from full swift test.
• Remove contradictory instructions.

Compare docs/versioning.md with the release and build guidance in README.md, docs/code-signing.md, docs/homebrew.md, and AGENTS.md, using the cited sections as the starting point. Update the documents so docs/versioning.md is canonical, DMG names and dispatch instructions agree, archive-free Swift target builds are distinct from full swift test, and no contradictions remain.