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/batch.ts

@@ -153,7 +153,7 @@ export async function registerBatchRoutes(app: FastifyInstance): Promise<void> {
                 processBuffer = await decodeHeic(processBuffer);
                 // Update extension to match decoded format (HEIC/HEIF → PNG)
                 const ext = processFilename.match(/\.[^.]+$/)?.[0];
-                if (ext) processFilename = processFilename.slice(0, -ext.length) + ".png";
+                if (ext) processFilename = `${processFilename.slice(0, -ext.length)}.png`;
               }
               if (!skipPreprocess) {
                 processBuffer = await autoOrient(processBuffer);

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 });
     }
   }
 

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

apps/api/src/routes/teams.ts

@@ -11,7 +11,7 @@ import { randomUUID } from "node:crypto";
 import { eq, sql } from "drizzle-orm";
 import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
 import { db, schema } from "../db/index.js";
-import { requireAdmin, requireAuth } from "../plugins/auth.js";
+import { requireAdmin } from "../plugins/auth.js";
 
 function validateTeamName(name: unknown): string | null {
   if (typeof name !== "string") return "Team name is required";

apps/api/src/routes/tool-factory.ts

@@ -156,7 +156,7 @@ export function createToolRoute<T>(app: FastifyInstance, config: ToolRouteConfig
         try {
           fileBuffer = await decodeHeic(fileBuffer);
           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.",

apps/api/src/routes/tools/color-adjustments.ts

@@ -1,7 +1,6 @@
 import {
   brightness as adjustBrightness,
   contrast as adjustContrast,
-  saturation as adjustSaturation,
   sharpen as adjustSharpen,
   colorChannels,
   grayscale,

apps/api/src/routes/tools/content-aware-resize.ts

@@ -65,7 +65,7 @@ export function registerContentAwareResize(app: FastifyInstance) {
         try {
           fileBuffer = await decodeHeic(fileBuffer);
           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/HEIF file",

apps/api/src/routes/tools/image-enhancement.ts

@@ -4,7 +4,6 @@ import sharp from "sharp";
 import { z } from "zod";
 import { autoOrient } from "../../lib/auto-orient.js";
 import { validateImageBuffer } from "../../lib/file-validation.js";
-import { sanitizeFilename } from "../../lib/filename.js";
 import { decodeHeic } from "../../lib/heic-converter.js";
 import { resolveOutputFormat } from "../../lib/output-format.js";
 import { createToolRoute } from "../tool-factory.js";

apps/api/src/routes/tools/passport-photo.ts

@@ -160,7 +160,7 @@ export function registerPassportPhoto(app: FastifyInstance) {
         if (validation.format === "heif") {
           fileBuffer = await decodeHeic(fileBuffer);
           const ext = filename.match(/\.[^.]+$/)?.[0];
-          if (ext) filename = filename.slice(0, -ext.length) + ".png";
+          if (ext) filename = `${filename.slice(0, -ext.length)}.png`;
         }
 
         // Auto-orient to fix EXIF rotation

apps/api/src/routes/tools/remove-background.ts

@@ -83,7 +83,7 @@ export function registerRemoveBackground(app: FastifyInstance) {
         if (validation.format === "heif") {
           fileBuffer = await decodeHeic(fileBuffer);
           const ext = filename.match(/\.[^.]+$/)?.[0];
-          if (ext) filename = filename.slice(0, -ext.length) + ".png";
+          if (ext) filename = `${filename.slice(0, -ext.length)}.png`;
         }
 
         // Auto-orient to fix EXIF rotation

apps/api/src/routes/tools/stitch.ts

@@ -205,8 +205,9 @@ export function registerStitch(app: FastifyInstance) {
 
       if (settings.cornerRadius > 0) {
         const meta = await sharp(result).metadata();
-        const w = meta.width!;
-        const h = meta.height!;
+        if (!meta.width || !meta.height) throw new Error("Cannot read image dimensions");
+        const w = meta.width;
+        const h = meta.height;
         const r = Math.min(settings.cornerRadius, Math.floor(Math.min(w, h) / 2));
 
         const mask = Buffer.from(