feat(launcher): show cover art icons in rofi history picker

- Add history-art.ts: materializeCoverArt extracts cover blobs from stats DB to ~/.cache/subminer/covers
- Query cover_blob_hash in history-db with fallback via shared anime_id
- Backfill cover hash from older rows of the same series in groupHistoryBySeries
- Pass icons to rofi via null-separator protocol (\0icon\x1f<path>)

launcher/history-art.ts

@@ -0,0 +1,126 @@
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { Database } from 'bun:sqlite';
+import { isReadonlyWalRetryError } from './history-db.js';
+
+const COVER_EXTENSIONS = ['.jpg', '.png', '.webp', '.gif'] as const;
+
+export function getDefaultCoverCacheDir(): string {
+  return path.join(os.homedir(), '.cache', 'subminer', 'covers');
+}
+
+export function detectImageExtension(blob: Buffer): string {
+  if (blob.length >= 8 && blob.subarray(0, 8).equals(Buffer.from('89504e470d0a1a0a', 'hex'))) {
+    return '.png';
+  }
+  if (blob.length >= 3 && blob[0] === 0xff && blob[1] === 0xd8 && blob[2] === 0xff) {
+    return '.jpg';
+  }
+  if (
+    blob.length >= 12 &&
+    blob.subarray(0, 4).toString('ascii') === 'RIFF' &&
+    blob.subarray(8, 12).toString('ascii') === 'WEBP'
+  ) {
+    return '.webp';
+  }
+  if (blob.length >= 4 && blob.subarray(0, 3).toString('ascii') === 'GIF') {
+    return '.gif';
+  }
+  return '.jpg';
+}
+
+function findCachedCover(cacheDir: string, hash: string): string | null {
+  for (const ext of COVER_EXTENSIONS) {
+    const candidate = path.join(cacheDir, `${hash}${ext}`);
+    try {
+      if (fs.statSync(candidate).size > 0) return candidate;
+    } catch {
+      // not cached with this extension
+    }
+  }
+  return null;
+}
+
+function queryCoverBlobs(
+  dbPath: string,
+  hashes: string[],
+  options: { readonly?: boolean; readwrite?: boolean; create?: boolean },
+): Map<string, Buffer> {
+  const blobs = new Map<string, Buffer>();
+  const db = new Database(dbPath, options);
+  try {
+    const hasBlobTable = db
+      .query(`SELECT 1 FROM sqlite_master WHERE type = 'table' AND name = 'imm_cover_art_blobs'`)
+      .get();
+    if (!hasBlobTable) return blobs;
+
+    const stmt = db.query<{ cover_blob: Uint8Array | null }>(
+      'SELECT cover_blob FROM imm_cover_art_blobs WHERE blob_hash = ?',
+    );
+    for (const hash of hashes) {
+      const row = stmt.get(hash);
+      if (row?.cover_blob && row.cover_blob.length > 0) {
+        blobs.set(hash, Buffer.from(row.cover_blob));
+      }
+    }
+    return blobs;
+  } finally {
+    db.close();
+  }
+}
+
+/**
+ * Ensures cover art blobs referenced by hash exist as image files in the cache
+ * directory, extracting missing ones from the stats database. Returns a map of
+ * blob hash to on-disk image path for every cover that could be materialized.
+ */
+export function materializeCoverArt(
+  dbPath: string,
+  hashes: Array<string | null | undefined>,
+  cacheDir: string = getDefaultCoverCacheDir(),
+): Map<string, string> {
+  const wanted = Array.from(new Set(hashes.filter((hash): hash is string => Boolean(hash))));
+  const resolved = new Map<string, string>();
+  if (wanted.length === 0) return resolved;
+
+  const missing: string[] = [];
+  for (const hash of wanted) {
+    const cached = findCachedCover(cacheDir, hash);
+    if (cached) {
+      resolved.set(hash, cached);
+    } else {
+      missing.push(hash);
+    }
+  }
+  if (missing.length === 0) return resolved;
+
+  let blobs: Map<string, Buffer>;
+  try {
+    try {
+      blobs = queryCoverBlobs(dbPath, missing, { readonly: true });
+    } catch (error) {
+      if (!isReadonlyWalRetryError(error, dbPath)) throw error;
+      blobs = queryCoverBlobs(dbPath, missing, { readwrite: true, create: false });
+    }
+  } catch {
+    return resolved;
+  }
+  if (blobs.size === 0) return resolved;
+
+  try {
+    fs.mkdirSync(cacheDir, { recursive: true });
+  } catch {
+    return resolved;
+  }
+  for (const [hash, blob] of blobs) {
+    const target = path.join(cacheDir, `${hash}${detectImageExtension(blob)}`);
+    try {
+      fs.writeFileSync(target, blob);
+      resolved.set(hash, target);
+    } catch {
+      // cache write failure just means no icon for this entry
+    }
+  }
+  return resolved;
+}