Redesign UI and fix several bugs

- Add navbar with login/logout, search form, and Find Link branding
- Clean up index page: search-only, examples behind ?debug=1
- Improve article page: remove debug clutter, named Wikipedia links, collapsible candidates
- Add SVG favicon (🔗 emoji)
- Fix diff CSS: compact layout, auto table layout to eliminate wide marker column gap
- Catch TokenRequestDenied in OAuth start and show error page
- Store username in session at login; clear bad session on API failure
- Raise NoMatch when diff is empty (edit already applied)

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

web_view.py

@@ -4,11 +4,13 @@ import html
 import itertools
 import json
 import re
+import sys
 import typing
 
 import flask
 import werkzeug
 from requests_oauthlib import OAuth1Session
+from requests_oauthlib.oauth1_session import TokenRequestDenied
 from werkzeug.wrappers.response import Response
 
 from add_links import api, core, mediawiki_api, mediawiki_oauth
@@ -118,17 +120,20 @@ def index() -> str | Response:
         url = flask.url_for("oauth_callback", **flask.request.args)  # type: ignore
         return flask.redirect(url)
 
-    examples = load_examples()
-    examples.sort(
-        key=lambda i: float(i["with_links"]) / float(i["total"]), reverse=True
-    )
-
     if q := flask.request.args.get("q"):
         if q_trimmed := q.strip():
             return flask.redirect(article_url(q_trimmed))
 
+    debug = flask.request.args.get("debug")
+    examples: list[dict[str, str | int]] = []
+    if debug:
+        examples = load_examples()
+        examples.sort(
+            key=lambda i: float(i["with_links"]) / float(i["total"]), reverse=True
+        )
+
     return flask.render_template(
-        "index.html", examples=examples, article_url=article_url
+        "index.html", examples=examples, article_url=article_url, debug=debug
     )
 
 
@@ -187,7 +192,12 @@ def start_oauth() -> Response:
 
     oauth = OAuth1Session(client_key, client_secret=client_secret, callback_uri="oob")
     oauth.headers.update({"User-Agent": api.ua})
-    fetch_response = oauth.fetch_request_token(request_token_url)
+    try:
+        fetch_response = oauth.fetch_request_token(request_token_url)
+    except TokenRequestDenied as e:
+        return flask.make_response(
+            flask.render_template("error.html", message=str(e)), 502
+        )
 
     flask.session["owner_key"] = fetch_response.get("oauth_token")
     flask.session["owner_secret"] = fetch_response.get("oauth_token_secret")
@@ -229,7 +239,8 @@ def oauth_callback() -> werkzeug.wrappers.response.Response:
     flask.session["owner_key"] = oauth_tokens.get("oauth_token")
     flask.session["owner_secret"] = oauth_tokens.get("oauth_token_secret")
 
-    print("login successful")
+    username = mediawiki_oauth.get_username()
+    print(f"login successful: {username}", file=sys.stderr)
 
     next_page = flask.session.get("after_login")
     return flask.redirect(next_page if next_page else flask.url_for("index"))