test: expand coverage across all layers -- 1,268 new tests, fix replace-color div-by-zero

14-agent parallel test expansion covering integration, unit, E2E, E2E-Docker,
cross-format matrix, adversarial, GUI navigation/tools/settings/visual/a11y/perf.

- Integration: expand 23 tool test files with HEIC, stress, batch, edge cases
- Unit: close coverage gaps in image-engine, stores, lib (metadata, auto-enhance,
  connection-store, lazy-with-retry, collage/file-store HEIC preview)
- AI bridge: 141 new tests for dispatcher buffering, crash recovery, OOM/segfault
- Cross-format: 794 parameterized tests (16 formats x 12 tools + no-crash matrix)
- Adversarial: memory stress (50x large file), zero-byte, corrupted headers, unicode
- E2E-Docker: expand 8 spec files with dimension verification, pipeline chains
- GUI E2E: tool UI settings/interactions for all 47 tools, remove all test.skip,
  RBAC per-role verification, visual screenshot naming, cross-browser smoke tests,
  a11y ARIA/focus/contrast, performance budgets, 15-tool stability test
- Fix: replace-color.ts tolerance=0 caused division-by-zero producing NaN pixels

Total: 8,958 tests passing across 202 files. Zero failures, zero skips.

tests/e2e/gui-tools-metadata.spec.ts

@@ -237,5 +237,15 @@ test.describe("GUI Metadata Tools", () => {
       // Info tool does not produce a downloadable result
       await expect(page.getByRole("link", { name: /download/i })).not.toBeVisible();
     });
+
+    test("submit disabled without file, enabled with file", async ({ loggedInPage: page }) => {
+      await page.goto("/info");
+
+      const submitBtn = page.getByTestId("info-submit");
+      await expect(submitBtn).toBeDisabled();
+
+      await uploadTestImage(page);
+      await expect(submitBtn).toBeEnabled();
+    });
   });
 });