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/pipeline.ts

@@ -106,7 +106,7 @@ export async function registerPipelineRoutes(app: FastifyInstance): Promise<void
         fileBuffer = await decodeHeic(fileBuffer);
         // Update filename extension to match the decoded format
         const ext = filename.match(/\.[^.]+$/)?.[0];
-        if (ext) filename = filename.slice(0, -ext.length) + ".png";
+        if (ext) filename = `${filename.slice(0, -ext.length)}.png`;
       } catch (err) {
         return reply.status(422).send({
           error: "Failed to decode HEIC file. Ensure libheif-examples is installed.",
@@ -513,7 +513,7 @@ export async function registerPipelineRoutes(app: FastifyInstance): Promise<void
             if (validation.format === "heif") {
               currentBuffer = await decodeHeic(currentBuffer);
               const ext = currentFilename.match(/\.[^.]+$/)?.[0];
-              if (ext) currentFilename = currentFilename.slice(0, -ext.length) + ".png";
+              if (ext) currentFilename = `${currentFilename.slice(0, -ext.length)}.png`;
             }
 
             // Normalize EXIF orientation