chore: ruff cleanup — fix 7 long-standing lint findings

Mechanical, no behavior change. `ruff check src/ tests/` now passes
with zero findings.

- cli.py:147 (SIM105) — replace `try/except SynologyError/pass` around
  the cleanup logout with `contextlib.suppress(SynologyError)`.
- compose.py:271 (B007) — drop the unused `i` from the env_list
  preview-detection loop (the apply loop below still uses enumerate).
- compose.py:329 (E501) — extract `verb = "Updated" if … else "Added"`
  into a local before the return so the f-string fits in 100 cols.
- images.py:237 (E501) — extract `stopped_name = in_use_stopped[0]`
  before the return and split the message across two f-strings.
- test_auth.py:38, 127, 140 (SIM117) — combine nested `with patch(…):`
  / `with pytest.raises(…):` into single parenthesised with-statements.

236 tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/mcp_synology_container/cli.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import asyncio
+import contextlib
 import json
 import logging
 import sys
@@ -144,10 +145,8 @@ async def _run_setup() -> None:
                 client.sid = sid
                 click.echo(click.style("Login successful!", fg="green"))
                 # Logout cleanly
-                try:
+                with contextlib.suppress(SynologyError):
                     await client.request("SYNO.API.Auth", "logout", version=6, params={})
-                except SynologyError:
-                    pass
             else:
                 click.echo(click.style("Login failed: no session ID returned.", fg="red"), err=True)
                 sys.exit(1)