The Port-with-Fallback inbound (commit 62fd9f9d) was confusing as a
standalone protocol — fallbacks belong on a regular VLESS/Trojan TCP-TLS
inbound, the way Xray models them natively. Rip out the entire feature
cleanly (no migration needed since it was never released): protocol
constant, fallback children DB table, FallbackService, 2 API endpoints,
all UI rows, related translations and api-docs. A native fallback flow
attached to VLESS/Trojan TCP-TLS/Reality will land in a follow-up commit.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Lets operators with large client counts or multi-node setups pick PostgreSQL
at install time without breaking the existing SQLite default. Backend is
selected at runtime via XUI_DB_TYPE/XUI_DB_DSN, a small dialect layer keeps
the five JSON_EXTRACT/JSON_EACH queries portable, and a new `x-ui migrate-db`
subcommand copies SQLite data into PostgreSQL in FK-aware order.
