fix(picture): normalize Try-On refs to clean RGB PNG before OpenAI call

gpt-image-1 answered the last Try-On attempt with
  invalid_image_file: Invalid image file or mode for image 2
because one of the references (face/body/garment) was in a format or
color mode OpenAI's edits endpoint rejects — typical culprits are
HEIC from iPhones, CMYK JPEG, palette-mode PNG, APNG, or JPEG with an
ICC profile gpt-image-1 doesn't honour. mana-media stores originals
verbatim so whatever the user uploaded is what we were forwarding.

Route the references through mana-media's existing on-the-fly
/transform endpoint (format=png, w/h=1024, fit=inside) which pipes
the buffer through sharp server-side. One call per ref, all run in
parallel, same latency budget as before. Output is guaranteed
- PNG / RGB (or RGBA if the source had alpha, which gpt-image-1 accepts),
- no more than 1024 px on the longest side → well under OpenAI's
  4 MB/image cap,
- aspect-ratio-preserving (fit=inside) so a portrait body photo
  doesn't get squished into a square.

New helper `getMediaBufferAsPng(mediaId, longestSide)` in lib/media.ts
encapsulates the transform-URL build. The Try-On path in the picture
route now uses it instead of `getMediaBuffer`; all Blob filenames
pin to `.png` since the buffer is already normalized.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/api/src/lib/media.ts

@@ -57,6 +57,34 @@ export async function getMediaBuffer(
 	return { buffer, mimeType };
 }
 
+/**
+ * Download a media file normalized to plain RGB PNG, max `longestSide`
+ * pixels on its longer edge (default 1024). Uses mana-media's `/transform`
+ * endpoint, which pipes the original through `sharp` server-side — that
+ * handles HEIC from iPhones, palette-mode PNGs, CMYK JPEGs, weird color
+ * profiles, and other formats OpenAI's gpt-image-1 rejects with
+ * `invalid_image_file` or `Invalid image file or mode`.
+ *
+ * `fit=inside` preserves aspect ratio (no distortion on portrait/landscape
+ * refs) and only caps the longer side, which keeps payloads comfortably
+ * under OpenAI's 4 MB/image limit without losing reference fidelity.
+ */
+export async function getMediaBufferAsPng(
+	mediaId: string,
+	longestSide = 1024
+): Promise<{ buffer: ArrayBuffer; mimeType: 'image/png' }> {
+	const base = getMediaClient()
+		.getOriginalUrl(mediaId)
+		.replace(/\/file$/, '/transform');
+	const url = `${base}?format=png&w=${longestSide}&h=${longestSide}&fit=inside`;
+	const res = await fetch(url);
+	if (!res.ok) {
+		throw new Error(`mana-media transform failed for ${mediaId}: HTTP ${res.status}`);
+	}
+	const buffer = await res.arrayBuffer();
+	return { buffer, mimeType: 'image/png' };
+}
+
 /**
  * Verify that every id in `mediaIds` is owned by `userId` under one of
  * the given app scopes. Throws `{ status: 404, missing }` when any id