feat(discord): add channel_prompts config

Add native Discord channel_prompts support with parent forum fallback,
ephemeral runtime injection, config migration updates, docs, and tests.

tests/hermes_cli/test_config.py

@@ -459,7 +459,7 @@ class TestCustomProviderCompatibility:
             migrate_config(interactive=False, quiet=True)
             raw = yaml.safe_load(config_path.read_text(encoding="utf-8"))
 
-        assert raw["_config_version"] == 17
+        assert raw["_config_version"] == 18
         assert raw["providers"]["openai-direct"] == {
             "api": "https://api.openai.com/v1",
             "api_key": "test-key",
@@ -606,6 +606,26 @@ class TestInterimAssistantMessageConfig:
             migrate_config(interactive=False, quiet=True)
             raw = yaml.safe_load(config_path.read_text(encoding="utf-8"))
 
-        assert raw["_config_version"] == 17
+        assert raw["_config_version"] == 18
         assert raw["display"]["tool_progress"] == "off"
         assert raw["display"]["interim_assistant_messages"] is True
+
+
+class TestDiscordChannelPromptsConfig:
+    def test_default_config_includes_discord_channel_prompts(self):
+        assert DEFAULT_CONFIG["discord"]["channel_prompts"] == {}
+
+    def test_migrate_adds_discord_channel_prompts_default(self, tmp_path):
+        config_path = tmp_path / "config.yaml"
+        config_path.write_text(
+            yaml.safe_dump({"_config_version": 17, "discord": {"auto_thread": True}}),
+            encoding="utf-8",
+        )
+
+        with patch.dict(os.environ, {"HERMES_HOME": str(tmp_path)}):
+            migrate_config(interactive=False, quiet=True)
+            raw = yaml.safe_load(config_path.read_text(encoding="utf-8"))
+
+        assert raw["_config_version"] == 18
+        assert raw["discord"]["auto_thread"] is True
+        assert raw["discord"]["channel_prompts"] == {}