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/components/db-viewer/TableTree.test.tsx

@@ -40,6 +40,23 @@ describe("TableTree", () => {
     expect(screen.getByText("Materialized View")).toBeInTheDocument();
   });
 
+  it("shows a distinct icon and label for views", () => {
+    useDbViewerStore.setState({
+      schemas: ["public"],
+      currentSchema: "public",
+      tables: [
+        {
+          name: "order_summary",
+          schema: "public",
+          table_type: "VIEW",
+        },
+      ],
+    });
+    render(<TableTree />);
+    expect(screen.getByText("order_summary")).toBeInTheDocument();
+    expect(screen.getByText("View")).toBeInTheDocument();
+  });
+
   it("opens a tab when table is clicked", async () => {
     const user = userEvent.setup();
     useDbViewerStore.setState({