feat: add AVIF output format support across 6 remaining tools (#85)

Closes #73

AVIF was already supported in the core engine, convert, compress,
optimize-for-web, upscale, erase-object, svg-to-raster, and
pdf-to-image tools. This adds AVIF as an output format option to
the 6 tools that were missing it: split, collage, stitch,
image-to-base64, noise-removal, and red-eye-removal.

For each tool, both the frontend format selector (with quality
slider for AVIF's lossy encoding) and the backend Zod schema +
Sharp .avif() encoding were updated. AVIF defaults: quality from
the user slider, effort 4 (balanced encode speed).

Also fixes pre-existing Biome formatting violations in 5 files
that were blocking a clean lint pass.

apps/web/src/stores/split-store.ts

@@ -18,7 +18,7 @@ interface SplitState {
   rows: number;
   tileWidth: number;
   tileHeight: number;
-  outputFormat: "original" | "png" | "jpg" | "webp";
+  outputFormat: "original" | "png" | "jpg" | "webp" | "avif";
   quality: number;
 
   // Image dimensions (set when image loads in the canvas)
@@ -36,7 +36,7 @@ interface SplitState {
   setRows: (n: number) => void;
   setTileWidth: (n: number) => void;
   setTileHeight: (n: number) => void;
-  setOutputFormat: (f: "original" | "png" | "jpg" | "webp") => void;
+  setOutputFormat: (f: "original" | "png" | "jpg" | "webp" | "avif") => void;
   setQuality: (q: number) => void;
   setImageDimensions: (d: { width: number; height: number } | null) => void;
   setProcessing: (p: boolean) => void;