docs: logo, security warning, emoji headings

- embed favicon.svg as a logo in the README
- add a prominent "no security — trusted networks only" callout
- sprinkle emoji through README/TODO/PLAN/NOTES headings; fix NOTES typo

TODO.md

@@ -1,22 +1,22 @@
-# TODO
+# 📋 TODO
 
 Longer-term items deferred from v1.
 
-## Auth & access control
+## 🔐 Auth & access control
 - Add short PIN per bar/tablet on first launch (currently no client auth).
 - Harden `/admin` beyond a single shared password (per-user, audit log).
 - Decide whether bartender identity should be tracked per transaction.
 
-## Features
+## ✨ Features
 - Custom price entry (free-form numpad amount as a line item, and/or per-drink price override).
 - Per-bar price overrides on top of the shared drink catalog (v1 is shared catalog + per-bar selection only).
 - Crew identification (which crew member took the freebie) beyond a flat "by crew" flag.
 - Backoffice: live transaction feed, per-drink charts, void/edit confirmed transactions.
 - Offline-capable client with sync queue (v1 is online-only).
 
-## UX / scaling
+## 📱 UX / scaling
 - Check what happens on the tablet UI when a bar has *many* drinks — current no-scroll grid divides the available height equally across rows, so tiles will shrink. Verify legibility/tap target size with 15–25 drinks; may need pagination, scrolling, or smaller-grid mode.
 
-## Ops
+## 🔧 Ops
 - Backup strategy for the SQLite file (cron + copy off-box).
 - Health check endpoint + simple status page on the tablet if server unreachable.