add readme with architecture diagram, cleanup dead code

- add readme.md with ASCII architecture diagram in details block
- remove jetstream connection (vestige from pre-tap architecture)
- remove loadUserVotes and poll.votes Map (unused)
- add [src] link to tangled in header
- add .wrangler to gitignore

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

readme.md

···
+# pollz
+
+polls on atproto
+
+```
+firehose → tap → backend (zig + sqlite) → frontend
+                      ↑
+              user's PDS (oauth)
+```
+
+## stack
+
+- [tap](https://github.com/bluesky-social/atproto/tree/main/packages/tap) - firehose sync
+- [zig](https://ziglang.org) + [httpz](https://github.com/ikskuh/http.zig) - backend
+- [atcute](https://github.com/mary-ext/atcute) - atproto client
+- [fly.io](https://fly.io) - backend hosting
+- [cloudflare pages](https://pages.cloudflare.com) - frontend hosting