feat(cli): add SQLite cache, shared solution runner, and submit command

apps/cli/pick.ts

@@ -1,70 +1,72 @@
 #!/usr/bin/env bun
 /**
  * Fuzzy-pick a LeetCode problem and scaffold it via leetcode-cli.
- * Problem index is fetched from leetcode.com and cached for 24h in .cache/.
+ *
+ * The problem index lives in the local SQLite cache (see db.ts), refreshed at
+ * most once per 24h; campaign problem descriptions from README.md are
+ * backfilled into the same db on the way. Problems that already have a
+ * numbered file under work/ are excluded from the picker — re-picking them
+ * would only clobber the existing scaffold.
  */
 import { autocomplete, cancel, isCancel, spinner } from "@clack/prompts";
-import { mkdir } from "node:fs/promises";
-import { join } from "node:path";
+import { basename, join } from "node:path";
+import { fetchDescription, problemDb, readmeSlugs, type Problem } from "./db";
 
 const ROOT = join(import.meta.dir, "..", "..");
-const CACHE_FILE = join(ROOT, ".cache", "leetcode-problems.json");
-const CACHE_TTL_MS = 24 * 60 * 60 * 1000;
+const WORK_DIR = join(ROOT, "work");
 
-interface Problem {
-  id: number;
-  title: string;
-  slug: string;
-  difficulty: "Easy" | "Medium" | "Hard";
-  paidOnly: boolean;
-}
+const db = problemDb();
 
-const DIFFICULTY = ["", "Easy", "Medium", "Hard"] as const;
-
-async function loadProblems(): Promise<Problem[]> {
-  const file = Bun.file(CACHE_FILE);
-  if (await file.exists()) {
-    const stale = Date.now() - file.lastModified > CACHE_TTL_MS;
-    if (!stale) return file.json();
-  }
+// ── problem index (24h TTL) ──────────────────────────────────────
 
+if (db.indexStale()) {
   const s = spinner();
   s.start("Fetching problem index from leetcode.com");
-  const res = await fetch("https://leetcode.com/api/problems/all/", {
-    headers: { "user-agent": "Mozilla/5.0" },
-  });
-  if (!res.ok) {
-    s.error(`Fetch failed: ${res.status} ${res.statusText}`);
-    process.exit(1);
+  try {
+    s.stop(`Indexed ${await db.refreshIndex()} problems`);
+  } catch (err) {
+    if (db.all().length === 0) {
+      s.error(`Fetch failed: ${err}`);
+      process.exit(1);
+    }
+    s.stop(`Index refresh failed (${err}) — using cached copy`);
   }
-  const data = (await res.json()) as {
-    stat_status_pairs: Array<{
-      stat: {
-        frontend_question_id: number;
-        question__title: string;
-        question__title_slug: string;
-      };
-      difficulty: { level: 1 | 2 | 3 };
-      paid_only: boolean;
-    }>;
-  };
-  const problems: Problem[] = data.stat_status_pairs
-    .map((p) => ({
-      id: p.stat.frontend_question_id,
-      title: p.stat.question__title,
-      slug: p.stat.question__title_slug,
-      difficulty: DIFFICULTY[p.difficulty.level] as Problem["difficulty"],
-      paidOnly: p.paid_only,
-    }))
-    .sort((a, b) => a.id - b.id);
-  s.stop(`Loaded ${problems.length} problems`);
-
-  await mkdir(join(ROOT, ".cache"), { recursive: true });
-  await Bun.write(CACHE_FILE, JSON.stringify(problems));
-  return problems;
 }
 
-const problems = await loadProblems();
+// ── description backfill for the campaign problems in README.md ──
+
+const missing = db.missingDescriptions(readmeSlugs(await Bun.file(join(ROOT, "README.md")).text()));
+if (missing.length > 0) {
+  const s = spinner();
+  s.start(`Caching ${missing.length} problem descriptions`);
+  let fetched = 0;
+  let failed = 0;
+  await Promise.all(
+    Array.from({ length: 6 }, async () => {
+      for (let slug = missing.shift(); slug; slug = missing.shift()) {
+        try {
+          const html = await fetchDescription(slug);
+          if (html !== null) db.saveDescription(slug, html);
+          s.message(`Caching problem descriptions (${++fetched})`);
+        } catch {
+          failed++; // left NULL — retried on the next run
+        }
+      }
+    }),
+  );
+  s.stop(failed ? `Cached ${fetched} descriptions (${failed} failed, will retry next run)` : `Cached ${fetched} problem descriptions`);
+}
+
+// ── exclude problems already picked or solved under work/ ────────
+
+const done = new Set<number>();
+for (const rel of new Bun.Glob("**/*.*").scanSync({ cwd: WORK_DIR })) {
+  const m = basename(rel).match(/^(\d+)\./);
+  if (m) done.add(Number(m[1]));
+}
+
+const problems = db.all().filter((p) => !done.has(p.id));
+db.close();
 
 const picked = await autocomplete<Problem>({
   message: "Pick a problem",