feat(cli): support github-copilot in provider logout

Logout previously claimed to support github-copilot in --help text but had
no registered handler, so `provider logout github-copilot` failed with
"Logout not implemented". Add the handler, sharing token deletion with the
codex flow via `_delete_oauth_files`. Tighten handler-table types, fix the
codex test fixture filename, and cover github-copilot plus the unknown
provider path.

nanobot/cli/commands.py

@@ -5,6 +5,7 @@ import os
 import select
 import signal
 import sys
+from collections.abc import Callable
 from contextlib import nullcontext, suppress
 from pathlib import Path
 from typing import Any
@@ -1487,8 +1488,13 @@ provider_app = typer.Typer(help="Manage providers")
 app.add_typer(provider_app, name="provider")
 
 
-_LOGIN_HANDLERS: dict[str, Any] = {}
-_LOGOUT_HANDLERS: dict[str, Any] = {}
+_LOGIN_HANDLERS: dict[str, Callable[[], None]] = {}
+_LOGOUT_HANDLERS: dict[str, Callable[[], None]] = {}
+
+_PROVIDER_DISPLAY: dict[str, str] = {
+    "openai_codex": "OpenAI Codex",
+    "github_copilot": "GitHub Copilot",
+}
 
 
 def _register_login(name: str):
@@ -1587,20 +1593,46 @@ def _logout_openai_codex() -> None:
         raise typer.Exit(1)
 
     storage = FileTokenStorage(token_filename=OPENAI_CODEX_PROVIDER.token_filename)
+    _delete_oauth_files(storage.get_token_path(), _PROVIDER_DISPLAY["openai_codex"])
+
+
+@_register_logout("github_copilot")
+def _logout_github_copilot() -> None:
+    """Clear local OAuth credentials for GitHub Copilot."""
+    try:
+        from nanobot.providers.github_copilot_provider import get_storage
+    except ImportError:
+        console.print("[red]GitHub Copilot provider unavailable. Ensure oauth-cli-kit is installed.[/red]")
+        raise typer.Exit(1)
+
+    storage = get_storage()
+    _delete_oauth_files(storage.get_token_path(), _PROVIDER_DISPLAY["github_copilot"])
+
+
+def _delete_oauth_files(token_path: Path, provider_label: str) -> None:
+    """Delete OAuth token and lock files, reporting the result."""
     removed_paths: list[Path] = []
-
-    for path in (storage.get_token_path(), storage.get_token_path().with_suffix(".lock")):
-        if path.exists():
+    skipped: list[tuple[Path, OSError]] = []
+    for path in (token_path, token_path.with_suffix(".lock")):
+        try:
             path.unlink()
-            removed_paths.append(path)
+        except FileNotFoundError:
+            continue
+        except OSError as exc:
+            skipped.append((path, exc))
+            continue
+        removed_paths.append(path)
 
-    if not removed_paths:
-        console.print("[yellow]! No local OAuth credentials found for OpenAI Codex[/yellow]")
+    if not removed_paths and not skipped:
+        console.print(f"[yellow]! No local OAuth credentials found for {provider_label}[/yellow]")
         return
 
-    console.print("[green]✓ Logged out from OpenAI Codex[/green]")
-    for path in removed_paths:
-        console.print(f"[dim]Removed: {path}[/dim]")
+    if removed_paths:
+        console.print(f"[green]✓ Logged out from {provider_label}[/green]")
+        for path in removed_paths:
+            console.print(f"[dim]Removed: {path}[/dim]")
+    for path, exc in skipped:
+        console.print(f"[yellow]! Could not remove {path}: {exc}[/yellow]")
 
 
 @_register_login("github_copilot")