Feature 3: Devlog-Archiv — Live-Listener + /devlog-backfill

- Webhook-Nachrichten im Devlog-Kanal werden automatisch in SQLite archiviert
  (devlog.py im EcoGame-Repo bleibt unverändert)
- /devlog-backfill (Admin): scannt die komplette Kanal-Historie in 100er-Blöcken
- Dedupe über Discord-Message-ID, Embeds werden mit Titel+Beschreibung erfasst
- Neue Intents: GuildMessages + MessageContent, neue Env-Var DEVLOG_CHANNEL_ID

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/db.js

@@ -23,6 +23,16 @@ db.exec(`
         received_at  TEXT NOT NULL DEFAULT (datetime('now'))
     );
     CREATE INDEX IF NOT EXISTS idx_commits_repo_time ON commits (repo, committed_at DESC);
+
+    CREATE TABLE IF NOT EXISTS devlogs (
+        message_id  TEXT PRIMARY KEY,
+        channel_id  TEXT NOT NULL,
+        content     TEXT NOT NULL,
+        author_name TEXT,
+        posted_at   TEXT NOT NULL,
+        archived_at TEXT NOT NULL DEFAULT (datetime('now'))
+    );
+    CREATE INDEX IF NOT EXISTS idx_devlogs_posted ON devlogs (posted_at DESC);
 `);
 
 const insertCommit = db.prepare(`
@@ -38,3 +48,13 @@ export const saveCommits = db.transaction((commits) => {
     }
     return inserted;
 });
+
+const insertDevlog = db.prepare(`
+    INSERT OR IGNORE INTO devlogs (message_id, channel_id, content, author_name, posted_at)
+    VALUES (@message_id, @channel_id, @content, @author_name, @posted_at)
+`);
+
+/** Devlog speichern — bereits bekannte Message-IDs werden ignoriert. Gibt true zurück, wenn neu. */
+export function saveDevlog(devlog) {
+    return insertDevlog.run(devlog).changes > 0;
+}