feat(cli): add solution activity tracking and ordering for test/submit commands

apps/cli/db.ts

@@ -10,6 +10,12 @@
  *     are ever fetched, and paid-only problems are skipped because GraphQL
  *     returns null content for them.
  *
+ * A `solutions` table tracks the lifecycle of each work/ file by LC number:
+ * `created_at` (backfilled from the file's birthtime on every picker run),
+ * `last_tested` and `last_submitted` (stamped on exit 0 of leetcode-cli).
+ * The test picker sorts by last_tested, the submit picker by created_at, and
+ * submit hides anything with a last_submitted.
+ *
  * Library: side-effect-free on import — nothing is opened or fetched until
  * problemDb() is called. Index upserts never touch the description column, so
  * a daily refresh cannot evict cached statements.
@@ -27,6 +33,13 @@ export interface Problem {
   paidOnly: boolean;
 }
 
+/** Lifecycle of one work/ solution, keyed by LC number. ISO timestamps. */
+export interface SolutionActivity {
+  createdAt: string;
+  lastTested: string | null;
+  lastSubmitted: string | null;
+}
+
 const DIFFICULTY = ["", "Easy", "Medium", "Hard"] as const;
 const INDEX_TTL_MS = 24 * 60 * 60 * 1000;
 
@@ -109,6 +122,13 @@ export function problemDb(path = DB_PATH) {
       paid_only   INTEGER NOT NULL,
       description TEXT
     );
+    CREATE TABLE IF NOT EXISTS solutions (
+      id             INTEGER PRIMARY KEY,
+      created_at     TEXT NOT NULL,
+      last_tested    TEXT,
+      last_submitted TEXT
+    );
+    DROP TABLE IF EXISTS submissions;
     CREATE TABLE IF NOT EXISTS meta (
       key   TEXT PRIMARY KEY,
       value TEXT NOT NULL
@@ -177,6 +197,37 @@ export function problemDb(path = DB_PATH) {
       db.query("UPDATE problems SET description = ?2 WHERE slug = ?1").run(slug, html);
     },
 
+    /** Per-solution lifecycle rows keyed by LC number. */
+    solutionActivity(): Map<number, SolutionActivity> {
+      const rows = db
+        .query<{ id: number; created_at: string; last_tested: string | null; last_submitted: string | null }, []>(
+          "SELECT id, created_at, last_tested, last_submitted FROM solutions",
+        )
+        .all();
+      return new Map(
+        rows.map((r) => [r.id, { createdAt: r.created_at, lastTested: r.last_tested, lastSubmitted: r.last_submitted }]),
+      );
+    },
+
+    /** Register a solution's creation time; existing rows are left alone. */
+    ensureSolution(id: number, createdAt: string): void {
+      db.query("INSERT INTO solutions (id, created_at) VALUES (?1, ?2) ON CONFLICT(id) DO NOTHING").run(id, createdAt);
+    },
+
+    markTested(id: number): void {
+      db.query(
+        `INSERT INTO solutions (id, created_at, last_tested) VALUES (?1, ?2, ?2)
+         ON CONFLICT(id) DO UPDATE SET last_tested = excluded.last_tested`,
+      ).run(id, new Date().toISOString());
+    },
+
+    markSubmitted(id: number): void {
+      db.query(
+        `INSERT INTO solutions (id, created_at, last_submitted) VALUES (?1, ?2, ?2)
+         ON CONFLICT(id) DO UPDATE SET last_submitted = excluded.last_submitted`,
+      ).run(id, new Date().toISOString());
+    },
+
     close(): void {
       db.close();
     },