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

src-tauri/src/models/mod.rs

@@ -3,15 +3,15 @@ pub mod connection;
 pub mod db_viewer;
 pub mod folder;
 pub mod recent;
+pub mod settings;
 pub mod ssh;
 pub mod tag;
-pub mod settings;
 
 pub use connection::{Connection, ConnectionInput};
-pub use recent::RecentConnection;
 #[allow(unused_imports)]
 pub use db_viewer::{Change, ColumnInfo, FilterRule, Pagination, QueryResult, SortRule, TableInfo};
 pub use folder::{Folder, FolderInput};
+pub use recent::RecentConnection;
 pub use settings::Settings;
 pub use ssh::SshConfig;
-pub use tag::{Tag, TagInput};
+pub use tag::{Tag, TagInput};