feat(batch-upload): bulk footage plate upload matched by filename

Adds a third section to the Batch Upload page that attaches plate movies to
shots derived from the filename: DH2_VFX_058_120_REF.mov becomes the plate
"REF" on shot DH2_VFX_058_120. Shot matching reuses findMatchingShotCode, so
it behaves like the rest of the page (case-insensitive, longest code wins,
underscore-boundary only) and the filename remainder becomes the label.

Bytes go straight to Hetzner via the existing presign endpoint since plates
are multi-GB, with XHR for per-file progress. Files whose shot already has a
plate of the same name are skipped so re-running a batch does not stack
duplicates.

Also resets the thumbnail and plate previews when the project changes — they
are resolved against a specific project, but only the version-upload flow was
being cleared.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/batch-upload-parser.ts

@@ -93,3 +93,67 @@ export function findMatchingShotCode(
   }
   return null;
 }
+
+// ── Footage plates ────────────────────────────────────────────────────────────
+
+/** Video extensions accepted by the footage plate batch upload. */
+export const PLATE_EXTS = new Set(["mov", "mp4", "m4v", "mxf", "avi", "mkv", "webm"]);
+
+const PLATE_CONTENT_TYPES: Record<string, string> = {
+  mov: "video/quicktime",
+  mp4: "video/mp4",
+  m4v: "video/mp4",
+  mxf: "video/mxf",
+  avi: "video/x-msvideo",
+  mkv: "video/x-matroska",
+  webm: "video/webm",
+};
+
+/**
+ * Derive a `video/*` content type from a plate filename's extension.
+ *
+ * Browsers routinely report an empty MIME type for .mov / .mxf files
+ * (especially on Windows), and the presign endpoint rejects anything that
+ * isn't `video/*`, so never trust `File.type` for these.
+ */
+export function plateContentType(fileName: string): string {
+  const ext = fileName.split(".").pop()?.toLowerCase() ?? "";
+  return PLATE_CONTENT_TYPES[ext] ?? "application/octet-stream";
+}
+
+export interface ParsedPlateFilename {
+  /** Lowercased extension without the leading dot */
+  ext: string;
+  /** Filename without the extension */
+  nameWithoutExt: string;
+  /** Shot code this file belongs to, or null when nothing matched */
+  shotCode: string | null;
+  /**
+   * The filename remainder after the shot code, used as the plate label.
+   * e.g. "DH2_VFX_058_120_REF.mov" → "REF".
+   * Empty when the filename is exactly the shot code.
+   */
+  label: string;
+}
+
+/**
+ * Resolve a footage plate filename to a shot code and a plate label.
+ *
+ * e.g. "DH2_VFX_058_120_REF.mov" against shot "DH2_VFX_058_120"
+ *      → { shotCode: "DH2_VFX_058_120", label: "REF" }
+ */
+export function parsePlateFilename(
+  fileName: string,
+  shotCodes: string[]
+): ParsedPlateFilename {
+  const lastDot = fileName.lastIndexOf(".");
+  const ext = lastDot >= 0 ? fileName.slice(lastDot + 1).toLowerCase() : "";
+  const nameWithoutExt = lastDot >= 0 ? fileName.slice(0, lastDot) : fileName;
+
+  const shotCode = findMatchingShotCode(nameWithoutExt, shotCodes);
+  const label = shotCode
+    ? nameWithoutExt.slice(shotCode.length).replace(/^[_\-\s]+/, "").trim()
+    : "";
+
+  return { ext, nameWithoutExt, shotCode, label };
+}