Ruff-Cleanup: ganzes MC2-Repo lint-grün + projekt-passende ruff.toml

Die Ampel-Nachruestung deckte 317/337 vorbestehende ruff-Verstoesse im ganzen Repo
auf. Aufgeraeumt:
- ruff.toml: intentionale Muster als Projekt-Politik ausgenommen (BLE001 blind-except,
  S110/S112 try-except-pass/continue, PLW1510 subprocess-best-effort, B008 FastAPI-
  Depends/File-Idiom, EXE001 Shebang, + wenige Stil-Regeln). __init__.py-Re-Exports
  geschuetzt (F401).
- ruff --fix: 128 mechanische (Import-Sortierung, PEP585/604-Annotationen, tote Imports,
  ueberfluessige noqa) auto-behoben.
- 12 echte Reste von Hand: PERF402/102, PLC3002 (Lambda->walrus), ISC004 (String-Concat
  geklammert), F841/RUF059 (ungenutzte Vars), PIE810 (startswith-Tuple), UP031 (f-string),
  UP035 (veraltete typing-Imports).
Ergebnis: 'ruff check .' = 0, 'compileall' grün. Kein Verhaltenswechsel (nur Stil/Modernisierung).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/services/jobengine.py

@@ -90,7 +90,7 @@ def _run_job(job_id: str, args: list[str], env: dict | None = None, sudo_passwor
             log_str = "\n".join(job["log"])
             if "a password is required" in log_str or "password" in log_str.lower() or "sudo:" in log_str:
                 job["sudo_failed"] = True
-    except Exception as exc:  # noqa: BLE001
+    except Exception as exc:
         _append_log(job, f"[mc] Fehler: {exc}")
         job["state"] = "failed"
         job["returncode"] = -1
@@ -101,7 +101,7 @@ def _run_job(job_id: str, args: list[str], env: dict | None = None, sudo_passwor
         if cb and job["state"] == "done":
             try:
                 cb()
-            except Exception as exc:  # noqa: BLE001
+            except Exception as exc:
                 _append_log(job, f"[mc] Nachbearbeitung-Fehler: {exc}")
 
 
@@ -136,7 +136,7 @@ def attach_download_progress(job_id: str, local_dir: str, total_bytes: int) -> N
                             j["rate_bps"] = rate
                             j["eta_s"] = int((total_bytes - cur) / rate)
                     prev_t, prev_b = now, cur
-            except Exception:  # noqa: BLE001
+            except Exception:
                 pass
             time.sleep(1.0)
         j = JOBS.get(job_id)
@@ -182,7 +182,7 @@ def cancel_job(job_id: str) -> bool:
     if proc is not None:
         try:
             proc.terminate()
-        except Exception:  # noqa: BLE001
+        except Exception:
             pass
     else:
         job["state"] = "canceled"