initial commit: live meeting transcription pipeline

Go orchestrator: spawns audiotee for capture (system audio + mic, two
tracks), segments with an energy-threshold VAD, transcribes each segment
via qwen-asr (subprocess per segment, vendored as a pinned git submodule
in third_party/qwen-asr), and serves the live transcript over SSE while
also writing it durably to a text file. Includes a glossary/prompt-leakage
guard (internal/asr/leak.go) that discards a segment if the model echoes
the biasing prompt instead of transcribing.

cmd/transcriptor-ai is the main orchestrator; cmd/transcript-tail is a
minimal terminal SSE client. See CLAUDE.md for the full architecture and
the reasoning behind each choice (Go over Python/Swift/Rust, SSE over
WebSocket, why the VAD is a hand-rolled heuristic, etc).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/transcript/writer.go

@@ -0,0 +1,49 @@
+package transcript
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"sync"
+)
+
+// FileWriter appends each Message to a text file as a human-readable line,
+// flushed to disk immediately. Unlike Broadcaster.Publish (which drops
+// messages for a slow/stalled SSE client on purpose), FileWriter never
+// drops — this is the durable record a crash shouldn't lose data from, so
+// every Write is synchronous and fsync'd before returning.
+type FileWriter struct {
+	mu sync.Mutex
+	f  *os.File
+}
+
+// NewFileWriter opens path for appending, creating it if needed. Appending
+// (not truncating) means restarting transcriptor-ai against the same path
+// continues the same transcript file rather than discarding it.
+func NewFileWriter(path string) (*FileWriter, error) {
+	f, err := os.OpenFile(path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return nil, fmt.Errorf("open transcript file: %w", err)
+	}
+	return &FileWriter{f: f}, nil
+}
+
+// Write appends one line for msg and fsyncs before returning.
+func (fw *FileWriter) Write(msg Message) error {
+	fw.mu.Lock()
+	defer fw.mu.Unlock()
+	line := fmt.Sprintf("[%s] [%s] %s\n", msg.Timestamp.Format("15:04:05"), msg.Track, msg.Text)
+	if _, err := io.WriteString(fw.f, line); err != nil {
+		return fmt.Errorf("write transcript line: %w", err)
+	}
+	if err := fw.f.Sync(); err != nil {
+		return fmt.Errorf("sync transcript file: %w", err)
+	}
+	return nil
+}
+
+func (fw *FileWriter) Close() error {
+	fw.mu.Lock()
+	defer fw.mu.Unlock()
+	return fw.f.Close()
+}