Refactor code editor out of main UI + PubMed FTP PDF + login token fix

- Move code editor to standalone page; remove from main index/app mode switcher
- Add diff-active tab highlight and diff bar CSS to styles
- Add markdown table styles for chat messages
- PubMed: try NCBI FTP link before Unpaywall for PDF download
- Login: also persist token to localStorage for cross-tab auth
- Update skills state and config

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

.claude/settings.local.json

@@ -202,7 +202,9 @@
       "Bash(midi2ly output.midi -o from_midi.ly)",
       "Bash(lilypond --pdf -o pdf_test input.ly)",
       "Bash(mktemp -d)",
-      "WebFetch(domain:pcsp.nationalregister.org)"
+      "WebFetch(domain:pcsp.nationalregister.org)",
+      "Bash(mkdir -p pptx)",
+      "Bash(mv sinus *)"
     ]
   },
   "ANTHROPIC_BASE_URL": "https://openrouter.ai/api",