Add TravelLine pull integration for NetUP: capture endpoint + tl_token

- New /travelline route: accepts all NetUP polls, logs them to in-memory
  ring buffer (GET /travelline/_log to inspect), responds with active
  reservations in a generic PMS format
- Migration 007: adds tl_token column to netup_settings
- PATCH netup/settings now saves tl_token; GET returns it
- TvWelcomePage: new TravelLine section with read-only API URL + copy
  button and token input field

Setup in NetUP: Integration type = TravelLine,
API URL = https://api.hotelsync.ru/travelline, Token = <tl_token>

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

backend/migrations/007_netup_tl_token.sql

@@ -0,0 +1,3 @@
+-- Add TravelLine integration token to netup_settings
+ALTER TABLE netup_settings ADD COLUMN IF NOT EXISTS tl_token TEXT NOT NULL DEFAULT '';
+CREATE INDEX IF NOT EXISTS idx_netup_settings_tl_token ON netup_settings(tl_token) WHERE tl_token != '';