robust charset decoding + retry-failed endpoint

- fix: fetch_mail crashed on MIME pseudo-encodings like 'unknown-8bit',
  'x-unknown', '8bit'. New _safe_decode helper maps those (and any
  LookupError from unknown codecs) to latin-1, which never fails on
  8-bit input. Used in _extract_body and _decode_header_value.
- Consequence of the crash: scheduler marked the affected UIDs as
  processed to avoid retry loops, so those mails never got sorted
  even after the underlying issue was fixable.
- feat: POST /api/filters/retry-failed drops the ProcessedMail markers
  for UIDs that appear in "Fehler beim Abrufen" error logs, so the
  next poll re-evaluates them. Reachable via a button in the log UI
  ("Fehlgeschlagene neu einlesen"), optionally scoped per account.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/routers/filters.py

@@ -5,7 +5,15 @@ from sqlalchemy.orm import Session
 import logging
 
 from app.database import get_db
-from app.models.db_models import Account, FilterAction, FilterCondition, FilterRule, ProcessedMail
+from app.models.db_models import (
+    Account,
+    FilterAction,
+    FilterCondition,
+    FilterLog,
+    FilterRule,
+    LogLevel,
+    ProcessedMail,
+)
 from app.schemas.schemas import FilterRuleCreate, FilterRuleResponse, FilterRuleUpdate
 
 logger = logging.getLogger(__name__)
@@ -25,6 +33,36 @@ def _reset_processed_for_rule(db: Session, rule_id: int) -> int:
 router = APIRouter(prefix="/api/filters", tags=["filters"])
 
 
+@router.post("/retry-failed")
+def retry_failed_fetches(account_id: int | None = None, db: Session = Depends(get_db)):
+    """Löscht ProcessedMail-Einträge für UIDs, für die es einen ERROR-Log
+    mit 'Fehler beim Abrufen' gibt — damit der Scheduler sie beim nächsten
+    Poll neu versucht (z.B. nach einem Codec-Fix)."""
+    log_q = db.query(FilterLog.mail_uid, FilterLog.account_id).filter(
+        FilterLog.level == LogLevel.ERROR,
+        FilterLog.message.like("Fehler beim Abrufen%"),
+        FilterLog.mail_uid.isnot(None),
+    )
+    if account_id is not None:
+        log_q = log_q.filter(FilterLog.account_id == account_id)
+
+    pairs = {(row[0], row[1]) for row in log_q.all()}
+    if not pairs:
+        return {"reset": 0, "unique_uids": 0}
+
+    total = 0
+    for uid, acc_id in pairs:
+        q = db.query(ProcessedMail).filter(ProcessedMail.mail_uid == uid)
+        if acc_id is not None:
+            q = q.filter(ProcessedMail.account_id == acc_id)
+        total += q.delete(synchronize_session=False)
+    db.commit()
+    logger.info(
+        "Retry-Failed: %d ProcessedMail-Einträge für %d UIDs entfernt", total, len(pairs)
+    )
+    return {"reset": total, "unique_uids": len(pairs)}
+
+
 @router.get("/account/{account_id}", response_model=list[FilterRuleResponse])
 def list_filters(account_id: int, db: Session = Depends(get_db)):
     account = db.get(Account, account_id)