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/terminalstate/tracker_test.go

@@ -0,0 +1,53 @@
+package terminalstate
+
+import "testing"
+
+func TestTrackerSnapshotChangeTracking(t *testing.T) {
+	tracker := NewTracker(10, 3)
+	if err := tracker.Feed([]byte("hi")); err != nil {
+		t.Fatalf("Feed() error = %v", err)
+	}
+
+	snapshot := tracker.Snapshot()
+	if !snapshot.HasChanges {
+		t.Fatalf("expected first snapshot to report changes")
+	}
+	if got := snapshot.Buffer[0][0].Data; got != "h" {
+		t.Fatalf("expected first cell to be h, got %q", got)
+	}
+	if got := snapshot.Buffer[0][1].Data; got != "i" {
+		t.Fatalf("expected second cell to be i, got %q", got)
+	}
+
+	again := tracker.Snapshot()
+	if again.HasChanges {
+		t.Fatalf("expected second snapshot without new input to report no changes")
+	}
+}
+
+func TestTrackerAnsiStyles(t *testing.T) {
+	tracker := NewTracker(10, 3)
+	if err := tracker.Feed([]byte("\x1b[31;1mA\x1b[0m")); err != nil {
+		t.Fatalf("Feed() error = %v", err)
+	}
+	snapshot := tracker.Snapshot()
+	cell := snapshot.Buffer[0][0]
+	if !cell.Bold {
+		t.Fatalf("expected bold attribute to be true")
+	}
+	if cell.FG != "red" {
+		t.Fatalf("expected red foreground, got %q", cell.FG)
+	}
+}
+
+func TestTrackerResize(t *testing.T) {
+	tracker := NewTracker(10, 3)
+	tracker.Resize(20, 4)
+	snapshot := tracker.Snapshot()
+	if snapshot.Width != 20 || snapshot.Height != 4 {
+		t.Fatalf("unexpected dimensions: got %dx%d", snapshot.Width, snapshot.Height)
+	}
+	if !snapshot.HasChanges {
+		t.Fatalf("expected resize to mark snapshot as changed")
+	}
+}