igdb: auto-refresh twitch token; category -> game_type filter

Static app tokens expire after ~60 days -> every lookup failed with
401. With igdb-client-secret set, the bot fetches the token via
client-credentials OAuth itself, refreshes a day before expiry and
retries once on 401; a static igdb-access-token still works.

IGDB renamed games.category to game_type: the category = 0 filter in
search_games silently matched nothing even with a valid token.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

IGDB_SETUP.md

@@ -20,13 +20,6 @@ The bot now supports real-time video game information through IGDB (Internet Gam
    - **Category**: Select appropriate category
 3. Note down your **Client ID**
 4. Generate a **Client Secret**
-5. Get an access token using this curl command:
-   ```bash
-   curl -X POST 'https://id.twitch.tv/oauth2/token' \
-   -H 'Content-Type: application/x-www-form-urlencoded' \
-   -d 'client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET&grant_type=client_credentials'
-   ```
-6. Save the `access_token` from the response
 
 ### 2. Configure the Bot
 
@@ -35,6 +28,25 @@ Update your `config.toml` file:
 ```toml
 # IGDB Configuration for game information
 igdb-client-id = "your_actual_client_id_here"
+igdb-client-secret = "your_actual_client_secret_here"
+enable-game-info = true
+```
+
+With the client secret configured, the bot fetches an app access token from
+Twitch itself and refreshes it automatically before it expires (Twitch app
+tokens live ~60 days) — no manual token handling needed.
+
+Alternatively, a static token still works (legacy setup — it expires after
+~60 days and then game lookups fail with 401 until you replace it):
+
+```bash
+curl -X POST 'https://id.twitch.tv/oauth2/token' \
+-H 'Content-Type: application/x-www-form-urlencoded' \
+-d 'client_id=YOUR_CLIENT_ID&client_secret=YOUR_CLIENT_SECRET&grant_type=client_credentials'
+```
+
+```toml
+igdb-client-id = "your_actual_client_id_here"
 igdb-access-token = "your_actual_access_token_here"
 enable-game-info = true
 ```
@@ -99,7 +111,8 @@ The integration provides two OpenAI functions:
    - Verify client ID and access token are set
 
 2. **Authentication errors**
-   - Regenerate access token (they expire)
+   - Prefer `igdb-client-secret` — the bot then refreshes tokens itself
+   - With a static `igdb-access-token`: regenerate it (they expire)
    - Verify client ID matches your Twitch app
 
 3. **No game results**