chore: release v2.0.0-alpha.12

[levifig]

Change

Release publication for docs/changes/20260719-path-stability-and-origin-hygiene/ (landed as PR #127).

What & Why

Version bump to 2.0.0-alpha.12, curated changelog, and synchronized build artifacts. Tag, GitHub Release, and Homebrew tap update follow post-merge via loaf release --post-merge.

Verification

• Full gate green on main at 38fa08b before branching (go vet, go test ./..., typecheck, build).
• Real-state dogfood completed before publication: 10 unknown-origin rows reclassified backup-first (backup loaf-20260720-120536-862453000.sqlite), doctor clean of relationship-origin diagnostics, five stale blockers closed, real Codex install repinned — 96 execpolicy prefixes, hook, and guidance all render /opt/homebrew/bin/loaf with zero Cellar paths.

Migration / breaking changes

None beyond PR #127's documented repair workflow.