Prepare Beta 2 maintainer acceptance

[WebCrew]

Refs #23

Summary

• prepares a non-overwriting v0.5.0-beta.2 unsigned prerelease from the completed Phase 1 foundation candidate
• makes preview tag and title explicit workflow inputs for future manual runs
• updates release notes for persistence, hierarchy/history hardening, desktop boundaries, visible errors and corrected packaged branding
• states the pending SignPath status without implying that this unsigned artifact is signed
• adds a concise repeatable Windows maintainer acceptance checklist
• links the checklist from testing, distribution, README and the remaining Phase 1 roadmap gate

Release behavior

Merging this PR changes the preview workflow on main, which intentionally triggers publication of the new Beta 2 prerelease. The workflow refuses to overwrite an existing tag.

Verification

• node scripts/check.cjs
• git diff --check

Phase 1 remains In Progress until the maintainer executes the checklist and records the result in #23.