feat(tool-youtube-transcript): YouTube transcription tool

New standard tool extension backed by a self-hosted transcriber service
(http://100.102.55.49:41090, Tailscale, no API key). One tool
youtube_transcript — fetches transcripts for YouTube videos. Returns
completed (full text + timestamped segments), queued/processing (position
+ ETA + .youtube_subtitles_pending retry convention), or failed (error).

Pure core: validateUrl + format* functions + truncateOutput. Injected
edge: TranscriptClient (injectable fetchFn, AbortSignal.any for
cancellation). concurrencySafe true, capabilities network. 30 tests.

Verified: tsc EXIT 0, 1152 vitest, biome clean (327 files). Boot smoke
clean.

1 files changed, 23 insertions, 0 deletions

diff --git a/packages/tool-youtube-transcript/src/index.ts b/packages/tool-youtube-transcript/src/index.ts
new file mode 100644
index 0000000..4fec6e4
--- /dev/null
+++ b/packages/tool-youtube-transcript/src/index.ts
@@ -0,0 +1,23 @@
+export {
+	createTranscriptClient,
+	DEFAULT_BASE_URL,
+	DEFAULT_TIMEOUT_MS,
+	type FetchLike,
+	type TranscriptClient,
+	type TranscriptClientDeps,
+} from "./client.js";
+export { activate, extension, manifest } from "./extension.js";
+export {
+	type CompletedResponse,
+	type FailedResponse,
+	formatCompleted,
+	formatFailed,
+	formatQueued,
+	formatTimestamp,
+	type QueuedResponse,
+	type TranscriptResponse,
+	type TranscriptSegment,
+	truncateOutput,
+} from "./format.js";
+export { createYoutubeTranscriptTool, type YoutubeTranscriptToolDeps } from "./tool.js";
+export { type ValidationError, validateUrl } from "./validate.js";