fix/macos launch (#18)

* fix: macOS Finder launch (store path, ad-hoc signing, vendored openssl)

- Store::open was resolving 'gridline.db' relative to the working directory;
  Finder/LaunchServices launches run with cwd=/ so the .expect() panicked
  (exit 101, silent 'app does nothing') before Tauri ever started. Open the
  store under app.path().app_data_dir() in setup instead (same dir as the
  demo DB), creating the dir when needed.
- Add bundle.macOS.signingIdentity "-" + hardenedRuntime false so the
  bundler ad-hoc signs the whole bundle. Previously only the inner binary
  got Xcode 16's linker-signed signature, which macOS treats as unsigned:
  quarantined downloads showed 'damaged and can't be opened', and after
  quarantine removal LaunchServices silently refused to spawn it.
- ssh2 now builds OpenSSL vendored (feature vendored-openssl): the release
  binary previously carried an absolute LC_LOAD_DYLIB to the build machine's
  /opt/homebrew/opt/openssl@3/lib, which dyld aborted on (and hardened
  runtime library-validation rejected even when present).
- README: document the macOS first-launch paths (right-click Open / xattr
  for the damaged-error case, re-run after every upgrade).
- release.yml: update SIGNING STATUS comment to reflect ad-hoc signing.

* chore: bump 0.7.8 -> 0.7.9 (release prep)

- Version sync across package.json, src-tauri/Cargo.toml, src-tauri/tauri.conf.json
- version.test.ts / bundle-config.test.ts / docs-coverage.test.ts expect 0.7.9
- README: both download tables -> v0.7.9 asset names; new v0.7.9 changelog entry;
  tag instructions -> v0.7.9; MAINTENANCE comment updated
- AGENTS.md maintenance note example -> v0.7.9
- ROADMAP: Shipped (0.7.9) section; Next up retitled (0.8.0) TBD

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Gridline",
-  "version": "0.7.8",
+  "version": "0.7.9",
   "identifier": "com.adrianbonpin.gridline",
   "build": {
     "beforeDevCommand": "bun run dev",
@@ -27,6 +27,10 @@
     "active": true,
     "targets": "all",
     "resources": ["resources/pg_tools/*", "resources/mysql_tools/*"],
+    "macOS": {
+      "signingIdentity": "-",
+      "hardenedRuntime": false
+    },
     "icon": [
       "icons/32x32.png",
       "icons/128x128.png",