fix(anime-settings): restore GET /api/nfo/{key}/content for 'View NFO XML' button

The Anime Settings page (src/server/web/static/js/pages/anime-settings.js)
calls GET /api/nfo/{key}/content from its 'View NFO XML' button, but that
endpoint was removed during the NFO refactor (commits 21af502, a8e5487).
The frontend was never updated, so every click on the button 404'd.

Fix:
- Add NfoContentResponse model (key, folder, content, file_size,
  last_modified) to src/server/models/nfo.py.
- Add GET /api/nfo/{key}/content handler to src/server/api/nfo.py that
  reads <anime_directory>/<folder>/tvshow.nfo and returns it as
  {"content": "<xml>", ...} — matching what anime-settings.js
  viewNfoContent() already expects (data.content).
- Expose viewNfoContent on AniWorld.AnimeSettingsManager so it is
  consistent with the other public methods and directly callable from
  tests / other modules.

Tests:
- tests/api/test_nfo_endpoints.py: 4 new tests (auth-required, happy
  path returning XML, 404 on unknown series, 404 on missing tvshow.nfo).
  Also remove the file-local autouse 'reset_auth' fixture that wiped
  the conftest's master-password setup and made any login-based test
  fail with a stale-hash 'invalid credentials' error — that fixture
  was pre-existing and is a no-op now that conftest.py handles reset.
- tests/frontend/unit/anime_settings.test.js: 3 new tests for
  viewNfoContent (URL + auth header, writes <pre>, error toast on
  404) and an assertion in the public-API surface test.

src/server/api/nfo.py

@@ -4,6 +4,7 @@ Provides endpoints for NFO settings, repair, and validation for anime series.
 """
 import logging
 import os
+from datetime import datetime
 from typing import Any, List, Optional
 
 from fastapi import APIRouter, Depends, HTTPException, status
@@ -11,6 +12,7 @@ from pydantic import BaseModel
 
 from src.config.settings import settings
 from src.server.models.nfo import (
+    NfoContentResponse,
     NfoRepairResponse,
     NfoSeriesSettings,
     NfoSettingsResponse,
@@ -406,6 +408,74 @@ async def validate_nfo(
         )
 
 
+@router.get("/{key}/content", response_model=NfoContentResponse)
+async def get_nfo_content(
+    key: str,
+    _auth: dict = Depends(require_auth),
+    anime_service: AnimeService = Depends(get_anime_service),
+) -> NfoContentResponse:
+    """Read and return the raw tvshow.nfo XML for a series.
+
+    Used by the Anime Settings page's "View NFO XML" button to display the
+    on-disk NFO contents inside a ``<pre>`` block. The XML is returned as
+    plain text inside a JSON wrapper so the same auth/header pipeline as the
+    other NFO endpoints can be reused.
+
+    Args:
+        key: Series unique key
+        _auth: Authentication dependency
+        anime_service: AnimeService dependency
+
+    Returns:
+        NfoContentResponse with raw XML in ``content``, the on-disk path,
+        file size and last-modified timestamp.
+
+    Raises:
+        HTTPException 404: If the series or its tvshow.nfo file is not found
+        HTTPException 400: If the series has no folder configured
+        HTTPException 503: If ``settings.anime_directory`` is not configured
+    """
+    series_data = await _get_series_data(anime_service, key)
+    if not series_data:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Series not found: {key}",
+        )
+
+    folder = series_data.get("folder", "")
+    if not folder:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Series has no folder configured: {key}",
+        )
+
+    nfo_path = _get_nfo_path(folder)
+    if not os.path.isfile(nfo_path):
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"No tvshow.nfo file found for series '{key}'",
+        )
+
+    try:
+        stat = os.stat(nfo_path)
+        with open(nfo_path, "r", encoding="utf-8") as f:
+            xml_text = f.read()
+    except OSError as exc:
+        logger.error("Failed to read NFO file %s: %s", nfo_path, exc)
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Failed to read NFO file: {exc}",
+        ) from exc
+
+    return NfoContentResponse(
+        key=key,
+        folder=folder,
+        content=xml_text,
+        file_size=stat.st_size,
+        last_modified=datetime.fromtimestamp(stat.st_mtime),
+    )
+
+
 @router.get("/needs-repair", response_model=NfoNeedsRepairListResponse)
 async def get_series_needing_repair(
     _auth: dict = Depends(require_auth),