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/RestorePage.tsx

@@ -239,14 +239,21 @@ export function RestorePage({ connectionId }: RestorePageProps) {
                                 </div>
 
                                 {/* Clean toggle */}
-                                <label className="flex items-center gap-2.5 cursor-pointer group">
+                                <label
+                                    className={`flex items-center gap-2.5 cursor-pointer group ${
+                                        format === "plain"
+                                            ? "opacity-40 pointer-events-none"
+                                            : ""
+                                    }`}
+                                >
                                     <input
                                         type="checkbox"
                                         checked={clean}
                                         onChange={(e) =>
                                             setClean(e.target.checked)
                                         }
-                                        className="rounded bg-surface border-border accent-accent w-4 h-4 cursor-pointer"
+                                        disabled={format === "plain"}
+                                        className="rounded bg-surface border-border accent-accent w-4 h-4 cursor-pointer disabled:cursor-not-allowed"
                                     />
                                     <span className="text-sm text-text-muted group-hover:text-text transition-colors">
                                         Clean{" "}
@@ -255,6 +262,13 @@ export function RestorePage({ connectionId }: RestorePageProps) {
                                         </code>
                                     </span>
                                 </label>
+                                {format === "plain" && (
+                                    <p className="text-[11px] text-text-muted/70 -mt-3">
+                                        Plain SQL restores run via psql and don't
+                                        support DROP-before-CREATE. Use Custom
+                                        Archive for clean restores.
+                                    </p>
+                                )}
                             </div>
 
                             {/* Destructive confirmation */}