v0.44.1: direct-DMG download button + reliable bundle signing

Docs/marketing patch: the "Download for Mac" button now downloads the DMG directly, and the desktop sign script retries throttled codesign calls (PRs #154, #156, #157). No app-binary change from v0.44.0.

Highlights

• Direct DMG download (#154, #157): the marketing hero and bottom CTA now lead with a Download for Mac button linking straight to the notarized DMG via the stable, version-less OpenKlip-macos-arm64.dmg asset on the latest release (releases/latest/download/…, served as an attachment). The old "Get started" buttons were dropped now that download is the primary action. Every release must publish that version-less alias or the button 404s — docs/desktop-packaging-runbook.md now documents the required publish step.
• Reliable bundle signing (#156): scripts/sign-desktop-bundle.sh now retries throttled codesign calls (5 attempts, linear backoff, exit-code check) instead of silently shipping unsigned binaries. --timestamp hits Apple's timestamp server, which throttles the ~13-binary signing burst; this was the second half of the #153 sign-script bug. Takes effect on the next real DMG rebuild.
• App binary: unchanged from v0.44.0. This release re-attaches v0.44.0's DMG (versioned + version-less alias); no new signed/notarized build was produced.
• Verification: bun test --isolate (2743 tests: 2729 pass, 14 skip); 98 MCP tools; 54 capabilities; 46 registry actions; bun run typecheck and bun run check clean.

Known gaps

See TODO.md. Notably: the version-less DMG alias is not enforced by CI, so a future release that forgets it silently breaks the download button; still Apple-Silicon-only, no Intel/universal build; no published latest.json updater feed.

Full changelog: CHANGELOG.md