initial: svc-proxy — UDP valve for Simple Voice Chat

Standalone Go service that routes SVC client traffic to per-server
backend voice endpoints, configured via pg LISTEN/NOTIFY (same channel
mc-router subscribes to). Each pg `servers` row with both
`voice_address` and `voice_proxy_port` set spawns a Valve: a public
UDP listener that maintains per-client ephemeral bridges to the
backend's SVC port.

Pieces:
  cmd/svc-proxy/main.go     entry; wires config, log fan-out,
                            bridge.Manager, pgsync, httpsrv
  internal/config/          DATABASE_URL + BIND_HOST +
                            BRIDGE_IDLE_TTL (default 1m) +
                            HTTP_ADDR (default :8081)
  internal/pgsync/          LISTEN automc_routes_changed; diff
                            desired/actual routes; emit Apply()
  internal/bridge/          Valve per public port; per-client
                            bridge with atomic up/down byte counters;
                            idle eviction every 15s against TTL
  internal/httpsrv/         operator UI — embedded single-page HTML
                            with active-connections table polled
                            every 1s + SSE log stream
                            (last 500 lines backlog on connect)

Reverse-proxied behind server-manager at /infra/svc-proxy/* — bind
internal-only addresses for production; auth is the dashboard's
Basic gate.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

go.sum

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