feat(files): add save-as-new vs overwrite choice for library file edits (#564)

Editing a file from the library used to silently supersede it: the worker auto-saved every result as a new version and the leaf-only listing hid the original, which read as a destructive overwrite. Tool pages now show a per-edit choice for library-sourced files. The default saves the result as an independent new file and keeps the original; picking overwrite keeps the old superseding-version behavior.

The client sends a saveMode multipart field next to fileId, validated with a 400 on unknown values, and autoSaveToLibrary branches on it. Every hand-written route that honors fileId parses the field the same way as the factory. The review panel shows where an auto-saved result went instead of offering a second, duplicate save. Tools whose route or submitter ignores fileId keep the selector hidden via a shared unsupported-tools set, and the choice resets to the non-destructive default whenever a new file is staged.

Closes #495

packages/shared/src/library-save.ts

@@ -0,0 +1,55 @@
+import { BASE_CONFIG, CONVERSION_PRESETS } from "./conversion-presets.js";
+
+/**
+ * Tools where the library save-mode choice (#495) does not work end to end,
+ * so the selector must stay hidden: either the tool's hand-written route
+ * ignores the multipart fileId/saveMode pair, or its settings component
+ * submits through its own XHR without sending them. For these tools a
+ * library-sourced edit is never auto-saved (the pre-#495 status quo).
+ *
+ * When wiring one of these up (parse fileId/saveMode in the route like
+ * tool-factory.ts, append them in the client like sign-pdf-settings.tsx),
+ * remove it from this set so the selector appears. The integration suite
+ * pins the other direction: every tool NOT listed here returns 400 for an
+ * invalid saveMode.
+ */
+export const LIBRARY_SAVE_MODE_UNSUPPORTED_TOOLS: ReadonlySet<string> = new Set([
+  // Custom routes without fileId/saveMode handling
+  "barcode-generate",
+  "barcode-read",
+  "beautify",
+  "bulk-rename",
+  "collage",
+  "color-palette",
+  "compare",
+  "compose",
+  "content-aware-resize",
+  "edit-metadata",
+  "favicon",
+  "find-duplicates",
+  "gif-tools",
+  "html-to-image",
+  "image-enhancement",
+  "image-to-base64",
+  "image-to-pdf",
+  "info",
+  "meme-generator",
+  "optimize-for-web",
+  "passport-photo",
+  "pdf-to-image",
+  "qr-generate",
+  "split",
+  "stitch",
+  "strip-metadata",
+  "vectorize",
+  "watermark-image",
+  // Routes accept saveMode but the custom client submitters do not send it yet
+  "ocr",
+  "remove-background",
+  "erase-object",
+  "background-replace",
+  "blur-background",
+  // Conversion presets served by the custom image-to-pdf / pdf-to-image /
+  // svg-to-raster routes (the registry group rides the factory and works)
+  ...CONVERSION_PRESETS.filter((p) => BASE_CONFIG[p.base]?.group !== "registry").map((p) => p.id),
+]);