feat(cli): emit anonymous usage events

[shfunc]

Note

Medium Risk
Introduces outbound network calls on every CLI invocation with privacy-sensitive design constraints; failures are isolated but the feature touches all CLI entry paths.

Overview
Adds anonymous CLI usage analytics separate from eval trace telemetry, controlled by HUD_CLI_ANALYTICS_ENABLED (opt out via hud set HUD_CLI_ANALYTICS_ENABLED=0).

Each CLI run records one background event to {HUD_TELEMETRY_URL}/sdk-events/cli with an allowlisted payload: registered command/subcommand names (argv is introspected so task files, trace IDs, and other positionals are never sent), exit code, error class, duration, SDK/Python/OS, CI flag, and a persisted anonymous install id in ~/.hud/.env. A one-time stderr notice appears when the install id is first created. Sends are daemon-threaded with a ~1.5s join cap and failures are suppressed so analytics cannot break commands.

The CLI entrypoint wraps execution in recorded_invocation. Unit tests disable CLI analytics in conftest. New Telemetry and analytics reference doc explains both telemetry and CLI analytics.

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