feat: complete Go port with go-te terminal emulator

Full Go implementation under go/ replacing Python pyte with go-te:
- HTTP server with WebSocket protocol, SSE, screenshot SVG rendering
- PTY terminal sessions and Docker exec sessions
- Docker watcher (label-based container discovery + event stream)
- CPU stats collection with sparkline SVG rendering
- Session manager with TwoWayMap routing and replay buffers
- C1 normalization, DA filtering, identity generation, theme palettes

Audit fixes for 9 concurrency/correctness issues:
- HTTP transport leak: shared client pool for Docker socket calls
- WebSocket concurrent writes: all writes routed through send channel
- Closed channel panic: atomic.Bool guard on enqueueWSData
- GetFirstRunningSession: use UnsafeForward under SessionManager lock
- NewSession TOCTOU: re-check routeKey after re-acquiring lock
- waitErr data race: protect with mutex in both session types
- Replay buffer fragmentation: copy to new slice on eviction
- go-te dirty tracking: check screen.Dirty before incrementing counter
- Identity modulo bias: rejection sampling for uniform distribution

All Go tests pass (including -race). Python baseline unchanged (397 tests).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

go/go.mod

@@ -0,0 +1,18 @@
+module github.com/rcarmo/webterm-go-port
+
+go 1.24.0
+
+require (
+	github.com/creack/pty v1.1.18
+	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
+	github.com/gorilla/websocket v1.5.3
+	github.com/rcarmo/go-te v0.0.0-20260214100434-edf070e453db
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require (
+	github.com/clipperhouse/uax29/v2 v2.2.0 // indirect
+	github.com/mattn/go-runewidth v0.0.19 // indirect
+	github.com/rivo/uniseg v0.4.7 // indirect
+	golang.org/x/text v0.34.0 // indirect
+)