Add accounts, presets, live sheet panel and equipment tiles

- Login with registration code, sessions, rate limiting, per-user characters
- Share characters with other users (read-only), admin CLI
- Rules presets with a Presets tab, applied/pending changes with diff in a side sheet
- Equipment as tiles with amounts, starting kit removed
- Rename nav tab to "Character", add "New character" button
- Stop tracking _to_delete/

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HJhXuLD2Z6hv3Wqeq9UL9K

.gitignore

@@ -5,3 +5,5 @@ backend/__pycache__/
 backend/app/__pycache__/
 backend/aw.db
 db/
+.env
+_to_delete/