feat(config): add /config TUI with tab-based settings and plugin config framework

- textual-based ConfigApp with General, Plugins, and per-plugin tabs
- GeneralConfig (user_name, assistant_name) + plugin_settings dict added to PyraConfig
- ConfigField dataclass and config_fields() method added to plugin protocol
- /config slash command in chat REPL launches the TUI
- pyra auto-runs setup wizard on first invocation when no config.yaml exists
- CLAUDE.md updated with config_fields() plugin guide and Code Inventory entries

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pyra/chat/session.py

@@ -33,6 +33,7 @@ _STATIC_COMMANDS = {
     "/exit": "Exit Pyra",
     "/clear": "Clear conversation history",
     "/memory list": "List memory files",
+    "/config": "Open configuration TUI",
     "/help": "Show available slash commands",
 }
 
@@ -198,6 +199,15 @@ def start_chat() -> None:
             _show_memory_list()
             continue
 
+        if user_input == "/config":
+            from pyra.config.tui import launch_config_tui
+            launch_config_tui()
+            try:
+                cfg = load_config()
+            except FileNotFoundError:
+                pass
+            continue
+
         if user_input in plugin_slash:
             try:
                 plugin_slash[user_input]()