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/lib.rs

@@ -2,16 +2,16 @@
 // of runtime usage, producing expected dead_code/unused warnings during development.
 #![allow(dead_code)]
 
+mod commands;
 mod db;
 mod models;
 mod store;
-mod commands;
 
-use std::sync::{Arc, Mutex as StdMutex};
-use tauri::Manager;
-use store::Store;
 use commands::ssh::{Ssh2Backend, SshTunnelManager};
 use db::pool::ConnectionPoolManager;
+use std::sync::{Arc, Mutex as StdMutex};
+use store::Store;
+use tauri::Manager;
 
 pub struct AppState {
     pub db_store: StdMutex<Store>,
@@ -19,7 +19,10 @@ pub struct AppState {
     pub ssh_manager: StdMutex<SshTunnelManager>,
 }
 
-use commands::{connections, db_viewer, folders, tags, settings, import_export, keychain, demo, backup, schema_graph, query};
+use commands::{
+    backup, connections, db_viewer, demo, folders, import_export, keychain, query, schema_graph,
+    settings, tags,
+};
 
 // Learn more about Tauri commands at https://tauri.app/develop/calling-rust/
 #[tauri::command]