test: expand API and GUI test coverage across all tools

Add ~500 new E2E tests and ~300 new integration tests covering:

- 24 new GUI E2E specs: navigation, responsive layout, keyboard shortcuts,
  tool UI for all 35 non-AI tools, batch/pipeline workflows, settings/RBAC,
  visual regression, accessibility, and performance budgets
- 3 new E2E-Docker specs: batch workflows, advanced pipelines, cross-format
- 1 new adversarial integration test: memory pressure, corrupted files,
  unicode filenames, extreme dimensions, pipeline/batch edge cases
- 29 expanded integration test files: HEIC/HEIF input, large files, parameter
  boundaries, batch processing, format edge cases across all tools
- Cross-format matrix expanded: 641 tests covering every tool x 18 formats
- AI bridge unit tests expanded: lifecycle, tool modules, error propagation
- Unit test gaps filled: analytics, tool-registry, web stores

Also fixes:
- vitest.config.ts: exclude e2e-docs and e2e-landing from Vitest runner
- AI E2E specs: add sidecar health check to skip gracefully when Python
  AI backend is not running instead of timing out

tests/e2e/remove-bg.spec.ts

@@ -1,5 +1,5 @@
 import path from "node:path";
-import { expect, test } from "./helpers";
+import { expect, isAiSidecarRunning, test } from "./helpers";
 
 // ---------------------------------------------------------------------------
 // Remove Background tool - comprehensive e2e tests.
@@ -40,6 +40,9 @@ test.describe("Remove Background tool", () => {
     } catch {
       test.skip(true, "background-removal feature bundle not installed");
     }
+    if (!(await isAiSidecarRunning(page))) {
+      test.skip(true, "AI sidecar not running");
+    }
   }
 
   test("page loads with correct UI sections", async ({ loggedInPage: page }) => {