feat: add tape identifier dropzone on /zxdb

Client computes MD5 + size in-browser, server action looks up
software_hashes to identify tape files against ZXDB entries.

- src/utils/md5.ts: pure-JS MD5 for browser (Web Crypto lacks MD5)
- src/app/zxdb/actions.ts: server action identifyTape()
- src/app/zxdb/TapeIdentifier.tsx: dropzone client component
- src/server/repo/zxdb.ts: lookupByMd5() joins hashes→downloads→entries
- src/app/zxdb/page.tsx: mount TapeIdentifier between hero and nav grid

opus-4-6@McFiver

src/server/repo/zxdb.ts

@@ -56,6 +56,7 @@ import {
   searchByMagrefs,
   referencetypes,
   countries,
+  softwareHashes,
 } from "@/server/schema/zxdb";
 
 export type EntrySearchScope = "title" | "title_aliases" | "title_aliases_origins";
@@ -2621,3 +2622,42 @@ export async function getIssue(id: number): Promise<IssueDetail | null> {
     })),
   };
 }
+
+// ----- Tape identification via software_hashes -----
+
+export type TapeMatch = {
+  downloadId: number;
+  entryId: number;
+  entryTitle: string;
+  innerPath: string;
+  md5: string;
+  crc32: string;
+  sizeBytes: number;
+};
+
+export async function lookupByMd5(md5: string): Promise<TapeMatch[]> {
+  const rows = await db
+    .select({
+      downloadId: softwareHashes.downloadId,
+      entryId: downloads.entryId,
+      entryTitle: entries.title,
+      innerPath: softwareHashes.innerPath,
+      md5: softwareHashes.md5,
+      crc32: softwareHashes.crc32,
+      sizeBytes: softwareHashes.sizeBytes,
+    })
+    .from(softwareHashes)
+    .innerJoin(downloads, eq(downloads.id, softwareHashes.downloadId))
+    .innerJoin(entries, eq(entries.id, downloads.entryId))
+    .where(eq(softwareHashes.md5, md5.toLowerCase()));
+
+  return rows.map((r) => ({
+    downloadId: Number(r.downloadId),
+    entryId: Number(r.entryId),
+    entryTitle: r.entryTitle ?? "",
+    innerPath: r.innerPath,
+    md5: r.md5,
+    crc32: r.crc32,
+    sizeBytes: Number(r.sizeBytes),
+  }));
+}