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/env-flags.ts

@@ -0,0 +1,40 @@
+import { DEFAULT_POSTHOG_API_KEY, DEFAULT_POSTHOG_HOST } from "./product-identity.js";
+
+function normalizeEnvValue(value: string | undefined): string | undefined {
+	return value?.trim().toLowerCase();
+}
+
+function isDisableFlag(value: string | undefined): boolean {
+	const normalized = normalizeEnvValue(value);
+	return normalized === "1" || normalized === "true";
+}
+
+function isTelemetryOptOutFlag(value: string | undefined): boolean {
+	const normalized = normalizeEnvValue(value);
+	return normalized === "0" || normalized === "false" || normalized === "no";
+}
+
+export function shouldDisablePostHog(): boolean {
+	return (
+		isDisableFlag(process.env["OMO_DISABLE_POSTHOG"]) ||
+		isTelemetryOptOutFlag(process.env["OMO_SEND_ANONYMOUS_TELEMETRY"]) ||
+		isDisableFlag(process.env["OMO_CODEX_DISABLE_POSTHOG"]) ||
+		isTelemetryOptOutFlag(process.env["OMO_CODEX_SEND_ANONYMOUS_TELEMETRY"])
+	);
+}
+
+export function getPostHogApiKey(): string {
+	const explicit = process.env["POSTHOG_API_KEY"];
+	if (explicit === undefined) {
+		return DEFAULT_POSTHOG_API_KEY;
+	}
+	return explicit.trim();
+}
+
+export function hasPostHogApiKey(): boolean {
+	return getPostHogApiKey().length > 0;
+}
+
+export function getPostHogHost(): string {
+	return process.env["POSTHOG_HOST"]?.trim() || DEFAULT_POSTHOG_HOST;
+}