test: massive test coverage expansion (+1,437 tests, 22 new files)

Expand test coverage across all layers via 14 parallel agents:

Unit tests (3,378 total, +534):
- First-ever AI sidecar tests (157 tests covering bridge lifecycle, all 12 tool modules)
- API route infrastructure (auth, pipeline, batch, settings, teams, roles, audit, api-keys, files, docs)
- Lib coverage improvements (audit 7%->95%, worker-pool 33%->100%)
- Web store/lib gap fills (features-store, tool-registry)

Integration tests (4,403 total, +903):
- Expanded 19 tool test files with parameter variations, format edge cases, boundary values
- Cross-format matrix: 290 tests covering 14 tools x 17 formats
- Adversarial/edge cases: 63 tests for extreme inputs, concurrent requests, corrupted files

E2E-Docker (125 new tests):
- Expanded 8 spec files + 1 new file covering all 49 tools
- Added HEIC/format handling, auth failures, download verification

GUI E2E (expanded 28 spec files):
- Navigation, responsive layout, keyboard shortcuts
- All 51 tool UIs with settings, processing, display modes
- Batch/pipeline workflows, settings/RBAC, visual regression
- Resilience, accessibility (ARIA, contrast, focus), performance budgets

tests/unit/api/filename.test.ts

@@ -73,7 +73,7 @@ describe("sanitizeFilename", () => {
   });
 
   it("truncates very long filenames over 200 bytes", () => {
-    const longName = "a".repeat(300) + ".png";
+    const longName = `${"a".repeat(300)}.png`;
     const result = sanitizeFilename(longName);
     expect(new TextEncoder().encode(result).length).toBeLessThanOrEqual(200);
     expect(result).toMatch(/\.png$/);
@@ -114,7 +114,7 @@ describe("sanitizeFilename", () => {
   });
 
   it("truncates long unicode filenames correctly", () => {
-    const longUnicode = "\u{1F600}".repeat(100) + ".png";
+    const longUnicode = `${"\u{1F600}".repeat(100)}.png`;
     const result = sanitizeFilename(longUnicode);
     expect(new TextEncoder().encode(result).length).toBeLessThanOrEqual(200);
     expect(result).toMatch(/\.png$/);