chore(release): point the macOS fallback script and docs at GitHub (#39)

`scripts/release-mac.sh` still targeted the retired Gitea release flow: it
looked for `.gitea/workflows/release.yml`, keyed off GITEA_SERVER/REPO_OWNER,
and created/uploaded assets with `tea`. Releases are GitHub-only now, so the
script uploads with `gh release upload --clobber` (a locally signed DMG pair
supersedes the CI-built ones, which the next draft publish then ships).

Also corrects the release docs, which contradicted each other: AGENTS.md said
macOS is built manually and never in CI, while README said CI signs it. In
reality the `release.yml` macOS jobs sign + notarize when the APPLE_* secrets
are present and log a `notice` when they are not — so the checklist now says to
read the run output before publishing a draft (verified on v0.8.1: stapler
validate + spctl report `source=Notarized Developer ID`), lists the local
`scripts/release-mac.sh` as the fallback, and documents the cask bump that the
`release: published` event triggers.

The "keep versions in sync" checklist was also incomplete and had already been
the source of drift: it missed `desktop/src-tauri/Cargo.lock` (only the
`gridline` entry — the sqlx family shares 0.8.x), `www/public/landing.js`, the
site changelog, `bundle-config.test.ts`, the two README banners and the
MAINTENANCE comment.

AGENTS.md

@@ -189,11 +189,13 @@ Direct pushes to `prod` will be bypassed only in emergencies; prefer the PR path
 **Releases are GitHub-only.** Tag `prod` and push the tag to the `github` remote — `git tag vN.M.N && git push github vN.M.N`. GitHub Actions (`release.yml`) builds installers for macOS (Apple Silicon + Intel), Windows, and Linux and opens a **draft** release (review + publish on GitHub). The Gitea tag arrives automatically via the `pre-push` hook (or `scripts/mirror-gitea.sh`) — never `git push origin vN.M.N` expecting a build, and never publish a release on Gitea.
 
 **Before tagging**, keep everything in sync:
-- Version number across `desktop/package.json`, `desktop/src-tauri/Cargo.toml`, `desktop/src-tauri/tauri.conf.json`, and `www/src/pages/index.astro` (the landing page version string)
-- `desktop/src/lib/version.test.ts` and `desktop/src/lib/docs-coverage.test.ts` if they assert the version
-- **README download links are static (versioned)** — both download tables (top **Download** section + **Which file should I download?**) link directly to the release-tag assets (`releases/download/v0.7.9/<file>`). tauri-action uses default versioned asset names (`Gridline_<ver>_aarch64.dmg`, `Gridline-<ver>-1.x86_64.rpm`, etc.) — update BOTH tables to the new names on every release (see the MAINTENANCE comment in README.md).
+- Version number across `desktop/package.json`, `desktop/src-tauri/Cargo.toml` (+ the `gridline` entry in `desktop/src-tauri/Cargo.lock` — run any `cargo metadata`/`cargo build` to sync it; do NOT blanket-replace `0.8.x` in the lock, the sqlx family shares that version), `desktop/src-tauri/tauri.conf.json`
+- Landing page version strings: `www/src/pages/index.astro` and `www/public/landing.js` (both carry a `const version`), plus the new entry at the top of `www/src/data/changelog.ts`
+- Tests that assert the version: `desktop/src/lib/version.test.ts`, `desktop/src/lib/bundle-config.test.ts`, `desktop/src/lib/docs-coverage.test.ts` (this one also asserts the README's asset names and the landing `const version`)
+- **README download links are static (versioned)** — both download tables (top **Download** section + **Which file should I download?**) link directly to the release-tag assets (`releases/download/v0.8.1/<file>`). tauri-action uses default versioned asset names (`Gridline_<ver>_aarch64.dmg`, `Gridline-<ver>-1.x86_64.rpm`, etc.) — update BOTH tables, the two "current release (**vX.Y.Z**)" banners, and the MAINTENANCE comment on every release.
 - **Bundled pg tools:** `tauri.conf.json` `bundle.resources` lists `resources/pg_tools/*`; the `release.yml` matrix builds/downloads + checksum-verifies the static binaries before the Tauri build step.
-- **macOS is Developer-ID signed + notarized** via `scripts/release-mac.sh` (built manually on Adrian's machine; not in CI). The script auto-detects the Developer ID identity from the login keychain, reads notarization credentials from `~/.config/gridline/notarize.env` (App Store Connect API key), and verifies codesign + stapled notarization before uploading. If the cert or credentials are missing it fails with setup instructions (see the README's "macOS signing & notarization" section).
+- **macOS is Developer-ID signed + notarized in CI** from the repository secrets (`APPLE_CERTIFICATE`, `APPLE_CERTIFICATE_PASSWORD`, `APPLE_SIGNING_IDENTITY`, `APPLE_API_KEY`, `APPLE_API_ISSUER`, `APPLE_API_KEY_CONTENT`, `KEYCHAIN_PASSWORD`) — the workflow logs a `notice` when they are absent and falls back to ad-hoc, so **check the run output before publishing a draft**. Verify a published DMG with `xcrun stapler validate <dmg>` plus `spctl --assess --type execute` on the `.app` inside (`source=Notarized Developer ID`). `scripts/release-mac.sh` is the **local fallback**: it auto-detects the Developer ID identity from the login keychain, reads notarization credentials from `~/.config/gridline/notarize.env`, signs + notarizes + staples both architectures, verifies the result, then uploads to the **GitHub** release with `gh release upload --clobber`.
+- **After publishing the draft**, the `release: published` event runs the cask bump (`HOMEBREW_TAP_DEPLOY_KEY` pushes `Casks/gridline.rb` to `AdrianBonpin/homebrew-gridline`). Verify the cask `version` + `sha256` match the published DMGs.
 
 ### Adding a Tauri Command