feat(omo-codex): wire Codex SessionStart telemetry for DAU/WAU/MAU

Adds a new Codex plugin component `telemetry` that emits a single
omo_codex_daily_active event (reason: session_start) from every Codex
SessionStart hook, with the same UTC-day deduplication, hashed
installation identifier, and four-flag opt-out as the install-time
event. Previously omo-codex telemetry only fired on install_completed,
so DAU/WAU/MAU under-reported real Codex usage.

- New plugin component packages/omo-codex/plugin/components/telemetry/
  mirrors the rules/comment-checker/lsp pattern: own src/, tsc build,
  vitest tests, package.json (posthog-node dep), hooks/hooks.json.
- src/codex-hook.ts wraps createPluginPostHog().trackActive(..., "session_start")
  with safeShutdown so Codex session startup never blocks on telemetry.
- Plugin root hooks.json + workspaces register the new component
  alongside rules and ultrawork on SessionStart.
- Aggregate test expectations updated to include the telemetry directory.
- cross-package-equivalence.test.ts pins product-identity constants and
  shouldDisablePostHog behavior to stay byte-equivalent between the CLI
  installer (src/telemetry/) and the plugin runtime
  (plugin/components/telemetry/src/), so the two PostHog sources never
  drift on event name, distinct_id base, dedup file path, or opt-out
  flags.
- PostHogActivityReason union in the CLI-side posthog.ts gains
  "session_start" so future CLI paths can emit the same reason without
  a type break.

packages/omo-codex/plugin/components/telemetry/src/cli.ts

@@ -0,0 +1,69 @@
+#!/usr/bin/env node
+import { stdin as processStdin, stdout as processStdout } from "node:process";
+
+import { type CodexSessionStartInput, runSessionStartHook } from "./codex-hook.js";
+
+const command = process.argv[2];
+const subcommand = process.argv[3];
+
+if (command === "hook" && subcommand === "session-start") {
+	await runHookCli();
+} else {
+	process.stderr.write("Usage: codex-telemetry hook session-start\n");
+	process.exitCode = 1;
+}
+
+async function runHookCli(): Promise<void> {
+	const raw = await readStdin();
+	if (raw.trim().length === 0) return;
+	const parsed = parseHookInput(raw);
+	if (!isCodexSessionStartInput(parsed)) return;
+	const output = await runSessionStartHook(parsed);
+	if (output.length > 0) {
+		processStdout.write(output);
+	}
+}
+
+function parseHookInput(raw: string): unknown | undefined {
+	try {
+		const parsed: unknown = JSON.parse(raw);
+		return parsed;
+	} catch {
+		return undefined;
+	}
+}
+
+function isCodexSessionStartInput(value: unknown): value is CodexSessionStartInput {
+	return (
+		isRecord(value) &&
+		value["hook_event_name"] === "SessionStart" &&
+		typeof value["session_id"] === "string" &&
+		isStringOrNull(value["transcript_path"]) &&
+		typeof value["cwd"] === "string" &&
+		typeof value["model"] === "string" &&
+		typeof value["permission_mode"] === "string" &&
+		typeof value["source"] === "string"
+	);
+}
+
+function isStringOrNull(value: unknown): value is string | null {
+	return typeof value === "string" || value === null;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+	return typeof value === "object" && value !== null && !Array.isArray(value);
+}
+
+function readStdin(): Promise<string> {
+	return new Promise((resolve, reject) => {
+		let data = "";
+		processStdin.setEncoding("utf8");
+		processStdin.on("data", (chunk: string) => {
+			data += chunk;
+		});
+		processStdin.once("error", reject);
+		processStdin.once("end", () => {
+			resolve(data);
+		});
+	});
+}