test: expand test coverage across unit, integration, e2e, and e2e-docker suites

Add ~210 new tests filling gaps identified by a comprehensive 14-agent
coverage audit. Unit+integration tests go from 9,388 to 9,484 (all passing).

Unit tests (+36):
- AI bridge: OOM fallback path, custom tier option
- Web lib: api-errors, format date/datetime, tool-i18n coverage

Integration tests (+19):
- Format matrix: ai-canvas-expand and find-duplicates added to cross-format matrix
- Adversarial: SVG XXE attacks, SQL injection in settings, request body size
  limits, race conditions with identical filenames

E2E Docker (+3):
- ai-canvas-expand tool coverage with HEIC input and edge cases

E2E GUI (~150+):
- Navigation: login rate limiting, ai-canvas-expand in parameterized list
- Responsive: dropzone visibility, text readability, dialog bounds at all viewports
- Keyboard: shortcuts verified from automate, files, tool, and fullscreen pages
- Tool UI: undo/state-reset for 16 tools, crop canvas drag handles, rotate/border
  live preview, linked aspect-ratio inputs for resize
- Batch: per-image undo isolation, batch compress/convert/rotate (not just resize)
- Pipeline: tool palette search, step collapse/expand visibility
- Settings: audit log entry verification, system settings persistence, teams CRUD,
  role permission toggling
- RBAC: user/editor 403 on roles/teams endpoints, privilege escalation prevention,
  cross-role tab parity documented as intentional
- Accessibility: skip-to-content link (WCAG 2.4.1), comprehensive color contrast
  for all headings/body/buttons in both themes with DOM-walking background detection
- Resilience: auth expiry 401 redirect, rate limit 429 handling
- Performance: JS heap memory stability for tool navigation, dialog cycling,
  upload/clear cycles, rapid page navigation

tests/unit/ai/background-removal.test.ts

@@ -472,6 +472,38 @@ describe("removeBackground", () => {
       expect(runPythonWithProgress).toHaveBeenCalledTimes(2);
     });
 
+    it("throws when OOM fallback succeeds at bridge level but Python returns success: false", async () => {
+      vi.mocked(runPythonWithProgress)
+        .mockRejectedValueOnce(new Error("Process killed (out of memory)"))
+        .mockResolvedValueOnce({
+          stdout: '{"success": false, "error": "u2net model corrupt"}',
+          stderr: "",
+        });
+      // Only one parseStdoutJson call happens: the first attempt rejects before parsing
+      vi.mocked(parseStdoutJson).mockReturnValueOnce({
+        success: false,
+        error: "u2net model corrupt",
+      });
+
+      await expect(
+        removeBackground(FAKE_INPUT, FAKE_OUTPUT_DIR, { model: "birefnet-general" }),
+      ).rejects.toThrow("u2net model corrupt");
+
+      expect(runPythonWithProgress).toHaveBeenCalledTimes(2);
+    });
+
+    it("uses fallback error message when OOM fallback returns success: false without error", async () => {
+      vi.mocked(runPythonWithProgress)
+        .mockRejectedValueOnce(new Error("Process killed (out of memory)"))
+        .mockResolvedValueOnce({ stdout: '{"success": false}', stderr: "" });
+      // Only one parseStdoutJson call happens: the first attempt rejects before parsing
+      vi.mocked(parseStdoutJson).mockReturnValueOnce({ success: false });
+
+      await expect(
+        removeBackground(FAKE_INPUT, FAKE_OUTPUT_DIR, { model: "birefnet-general" }),
+      ).rejects.toThrow("Background removal failed");
+    });
+
     it("retries with fallback when no model is specified (default)", async () => {
       vi.mocked(runPythonWithProgress)
         .mockRejectedValueOnce(new Error("Process killed (out of memory)"))

tests/unit/ai/outpaint.test.ts

@@ -93,6 +93,45 @@ describe("outpaint", () => {
       );
     });
 
+    it("passes custom tier value instead of default 'balanced'", async () => {
+      const options: OutpaintOptions = {
+        extendTop: 10,
+        extendRight: 20,
+        extendBottom: 30,
+        extendLeft: 40,
+        tier: "high",
+      };
+      await outpaint(FAKE_INPUT, options, FAKE_OUTPUT_DIR);
+
+      expect(runPythonWithProgress).toHaveBeenCalledWith(
+        "outpaint.py",
+        [
+          `${FAKE_OUTPUT_DIR}/input_outpaint.png`,
+          `${FAKE_OUTPUT_DIR}/output_outpaint.png`,
+          "10",
+          "20",
+          "30",
+          "40",
+          "high",
+        ],
+        expect.any(Object),
+      );
+    });
+
+    it("passes 'fast' tier value", async () => {
+      const options: OutpaintOptions = {
+        extendTop: 5,
+        extendRight: 5,
+        extendBottom: 5,
+        extendLeft: 5,
+        tier: "fast",
+      };
+      await outpaint(FAKE_INPUT, options, FAKE_OUTPUT_DIR);
+
+      const args = vi.mocked(runPythonWithProgress).mock.calls[0][1];
+      expect(args[6]).toBe("fast");
+    });
+
     it("converts input to PNG via sharp", async () => {
       const options: OutpaintOptions = {
         extendTop: 0,