v0.6.0: release workflow, constraint-aware cell editing, pending-cell styling (#9)

* feat: demo DB seed/regenerate, backup/restore/sync refinements, SSH/SSL polish

- Demo SQLite DB: feature-rich seed (12 objects, 500-row audit log) + regenerate action in Settings
- Backup/restore: headless-testable core logic, psql -f for plain dumps, sync passes --clean --if-exists
- SSH/SSL runtime refinements and connection testing improvements
- Data grid: DataTypeIcon component, FK popover, table tree polish
- Docs: AGENTS.md/README updates, new screenshots, MIT LICENSE

* chore: optimize README screenshots (4.7 MB → 916 KB via pngquant, quality 70-90)

* v0.6.0: release workflow, constraint-aware cell editing, pending-cell styling

- Bump version to 0.6.0 across package.json, Cargo.toml, tauri.conf.json
- Add .github/workflows/release.yml: tag-triggered CI builds macOS (aarch64
  + x64), Windows, and Linux installers into a draft GitHub Release
- README: installer download table (unsigned note, per-platform files),
  "how releases are made" section
- CellEditor: constraint-aware commit — empty input on nullable columns
  becomes NULL, NOT NULL text-like types fall back to empty string, all
  other types blocked with an inline error bubble; replace "Set NULL"
  checkbox with a NULL row in the FK dropdown / empty enum option
- VirtualDataGrid: pending-edit dot → animated pending outline (ring) on
  staged cells; matching test updates
- docs-coverage test: align with rewritten README comparison table

AGENTS.md

@@ -284,11 +284,11 @@ cargo test               # Rust tests
 ### Backup & Restore
 | Feature | Status | Details |
 | :--- | :---: | :--- |
-| pg_dump wrapper | ✅ | Rust command spawns pg_dump with real-time progress events (backup-progress) |
-| pg_restore wrapper | ✅ | Rust command spawns pg_restore with progress events |
+| pg_dump wrapper | ✅ | Rust command spawns pg_dump with real-time progress events (backup-progress). Core logic extracted into headless-testable `run_pg_dump` (takes `PgConnParams` + options directly); Tauri command is a thin wrapper (store lookup → keychain → run → emit). Live integration tests in `backup.test.rs` (`#[ignore]`d, driven by `GRIDLINE_TEST_SRC_*`/`GRIDLINE_TEST_TGT_*` env vars) |
+| pg_restore wrapper | ✅ | Rust command spawns pg_restore with progress events. **Plain-format dumps are executed via `psql -f`** (pg_restore can't read plain SQL text); custom/tar/directory use pg_restore. Core logic in headless-testable `run_pg_restore` |
 | Backup UI | ✅ | In-page view: format selector, file browse (Tauri dialog), schema dropdown, no-owner toggle, progress bar with event-driven status |
-| Restore UI | ✅ | In-page view: file browse, format, clean toggle, destructive confirmation checkbox, progress bar |
-| DB-to-DB sync | ✅ | In-page view: source/target connection pickers, schema dropdown, pipe-based pg_dump → pg_restore |
+| Restore UI | ✅ | In-page view: file browse, format, clean toggle, destructive confirmation checkbox, progress bar. **Clean toggle is disabled for plain format** (psql can't DROP-before-CREATE) with a hint to use Custom Archive |
+| DB-to-DB sync | ✅ | In-page view: source/target connection pickers, schema dropdown, pipe-based pg_dump → pg_restore. **pg_restore side passes `--clean --if-exists`**, so sync works into a non-empty target (UI already requires destructive-overwrite confirmation). Core logic in headless-testable `run_db_sync` |
 | Unified Tools view | ✅ | Backup / Restore / DB Sync merged into a single **Tools** nav item; operation-switcher dropdown in the view toolbar, existing forms rendered below |
 | SQLite .dump | ❌ | |
 | Table structure export (DDL) | ❌ | |