fix(lint): resolve all biome warnings across API, web, and image-engine

API:
- Replace string concatenation with template literals (batch, pipeline,
  tool-factory, content-aware-resize, passport-photo, remove-background)
- Remove unused imports (teams, color-adjustments, image-enhancement)
- Replace non-null assertions with guard clauses in bg-effects and stitch
- Use optional chaining in docs route

Image-engine:
- Remove unused OutputFormat imports (compress, convert)
- Use local variables instead of reassigning parameters (optimize-for-web, sharpen)

Web:
- Fix useExhaustiveDependencies: remove genuinely redundant deps, add
  biome-ignore comments for intentional patterns (src prop, cleanup fns)
- Replace non-null assertions with null-safe alternatives
- Add accessible titles to inline SVGs (color-settings, image-enhancement-settings)
- Fix noLabelWithoutControl: associate labels via htmlFor/id or use <span>
  (image-to-base64-settings, edit-metadata-settings, qr-generate-settings)
- Replace div[role="button"] with <button> (pdf-to-image-settings)
- Use stable keys instead of array indices (collage-preview, collage-settings)
- Fix noStaticElementInteractions in collage-preview (role="none")
- Remove unused function parameters and imports

apps/api/src/routes/docs.ts

@@ -81,7 +81,7 @@ function generateLlmsFullTxt(spec: OpenAPISpec): string {
     for (const [method, op] of Object.entries(methods)) {
       const tag = op.tags?.[0] || "Other";
       if (!tagGroups.has(tag)) tagGroups.set(tag, []);
-      tagGroups.get(tag)!.push({ method: method.toUpperCase(), path, op });
+      tagGroups.get(tag)?.push({ method: method.toUpperCase(), path, op });
     }
   }