chore(release): v0.8.2 (#43)

Version bump 0.8.1 -> 0.8.2 across the app shell, the website and the README, plus v0.8.2 changelog entries for the native MySQL execution work merged in #42.

- desktop/package.json, desktop/src-tauri/Cargo.toml, desktop/src-tauri/tauri.conf.json, Cargo.lock (cargo-regenerated; gridline only - webview2-com-macros stays 0.8.1)
- www/public/landing.js + www/src/pages/index.astro const version; new top entry in www/src/data/changelog.ts
- version.test.ts, bundle-config.test.ts, docs-coverage.test.ts updated to 0.8.2
- README: both banners, both download tables (asset names + tags, incl. apt/dnf strings), MAINTENANCE comment, new v0.8.2 bullet

Verified: cargo build (gridline v0.8.2) + cargo test --lib 442 passed / 0 failed; bun run test 133 files / 1151 tests exit 0; tsc clean.

www/public/landing.js

@@ -60,7 +60,7 @@
     const keepLabel = downloadBtn.hasAttribute("data-download-label");
 
     const releasesUrl = "https://github.com/AdrianBonpin/gridline/releases";
-    const version = "0.8.1";
+    const version = "0.8.2";
 
     if (isMobile) {
       downloadBtn.href = releasesUrl;