feat: Enhance Mattermost extractor to support channel names and improve configuration options

scripts/mattermost/README.md

@@ -19,6 +19,30 @@ This directory contains the workspace-local Mattermost extractor used by OpenCod
 2. Fill in your Mattermost values.
 3. Create a local virtual environment if you want an isolated runtime.
 
+Preferred channel config:
+
+- `CHANNELS=fidelity-preguntas`
+
+Channel names are preferred for AI context because the exported records will use the readable channel name instead of the raw channel ID.
+
+The script can resolve channel names without a team if the authenticated user can access the channel and the name is unique across the user's teams.
+
+Supported env options:
+
+- `CHANNELS`
+  Mixed list of channel names or channel IDs.
+- `CHANNEL_NAMES`
+  Channel names only.
+- `CHANNEL_IDS`
+  Legacy channel IDs only.
+
+Optional only for disambiguation:
+
+- `MATTERMOST_TEAM_NAME`
+- `MATTERMOST_TEAM_ID`
+
+Use one of those only if the same channel name exists in multiple teams or if you want to force team-specific resolution.
+
 Example:
 
 ```bash