Fix User-Agent header, timeouts, and JSON error handling

mediawiki_oauth: set User-Agent on all OAuth1Session instances so
Wikimedia doesn't reject token and API requests with 403; add timeout
parameter to api_post_request (default 4s).

mediawiki_api: add APIError exception; wrap .json() in call() to raise
APIError with status code and response body on decode failure; raise
timeout to 30s for edit POSTs.

api: wrap call_get_diff .json() with the same JSONDecodeError guard,
raising MediawikiError with HTTP status and body on failure.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

add_links/mediawiki_api.py

@@ -4,8 +4,14 @@ import typing
 from pprint import pprint
 from typing import Any, cast
 
+import requests
+
 from . import mediawiki_oauth
 
+
+class APIError(Exception):
+    """Unexpected response from the MediaWiki API."""
+
 wiki_hostname = "en.wikipedia.org"
 wiki_api_php = f"https://{wiki_hostname}/w/api.php"
 user_agent = "add-links/0.1"
@@ -27,10 +33,13 @@ def parse_page(enwiki: str) -> dict[str, Any]:
     return parse
 
 
-def call(params: dict[str, str | int]) -> dict[str, typing.Any]:
+def call(params: dict[str, str | int], timeout: int = 4) -> dict[str, typing.Any]:
     """Make GET request to mediawiki API."""
-    data = mediawiki_oauth.api_post_request(params)
-    return cast(dict[str, Any], data.json())
+    r = mediawiki_oauth.api_post_request(params, timeout=timeout)
+    try:
+        return cast(dict[str, Any], r.json())
+    except requests.exceptions.JSONDecodeError:
+        raise APIError(f"HTTP {r.status_code}: {r.text[:200]!r}")
 
 
 def article_exists(title: str) -> bool:
@@ -92,7 +101,7 @@ def edit_page(
         "summary": summary,
         "section": section,
     }
-    ret = call(params)
+    ret = call(params, timeout=30)
     if "edit" not in ret:
         print("params")
         pprint(params)