[rushd][WS4] CLI client & command surface

[bmiddha]

Build the separate CLI client package/bin (@rushstack/rush-cli-client on @rushstack/rush-client-core) and its command surface — fallback/opt-in routing, rush daemon subcommands, the rush.json daemon config block + env overrides, an experimental rush daemon graph reference client, and a standalone rushx-equivalent bin — all opt-in until cutover.

Depends on: #5896; #5897; #5898

Scope

• rush-client-core + rush-cli-client bin. Connect/forward/pump, the request envelope (argv, cwd, env, columns, colorLevel), stream pumping, exit-code relay, and cancel-on-signal — with no SIGWINCH forwarding (the client owns width/resize).
• Fallback/opt-in routing. Decide daemon vs in-process per invocation from RUSH_DAEMON, --no-daemon, rush.json config, CI detection, and the never-daemonize list (routing to today's in-process path otherwise).
• rush.json daemon config. A validated daemon block (enabled, idleTimeoutSeconds, autoStart, watch, queueTimeoutSeconds, plus the WS3 warm-set knobs) with RUSH_DAEMON* env overrides.
• rush daemon subcommands. start|stop|restart|status|logs (themselves never-daemonized); status surfaces warm-set + lifecycle info (uptime, PID, reload tier, warm projects, memory) and logs streams the daemon log.
• Experimental rush daemon graph. Behind RUSH_DAEMON_EXPERIMENTAL=1, show/status/scope-in/scope-out/invalidate/watch/pause/resume over the warm graph, serving as a reference "third client" that consumes only structured events.
• Standalone rushx-equivalent. Run the cwd project's package script with the same auto-start/forward behavior; it becomes rushx at cutover (WS5).

Acceptance criteria

• The client connects, sends the request envelope, pumps stdout/stderr/stdin, and relays the daemon's exit code; Ctrl+C cancels the request; SIGWINCH is handled client-side and not forwarded; a sample rush build via the client is behaviorally equivalent to in-process (full matrix in WS5).
• Each routing input (RUSH_DAEMON, --no-daemon, config, CI, never-daemonize) selects the correct path with a documented precedence order; CI defaults to in-process (no auto-start) unless explicitly opted in.
• The rush.json daemon schema is published and validates the block (rejecting unknown/invalid values) with precedence env > config > default.
• Each rush daemon subcommand acts against a running (or absent) daemon with correct exit codes; status reports warm-set + lifecycle info and logs streams the daemon log (see WS5).
• The experimental rush daemon graph verbs operate over the warm graph via the protocol only (no rush-lib-internal calls), consume only the presentation-free event contract, and stay gated off unless RUSH_DAEMON_EXPERIMENTAL=1.
• The standalone rushx-equivalent resolves the project by cwd, forwards with auto-start, and matches today's rushx output/exit code for a sample script.
• rush-client-core has no rush-lib dependency and commits its API Extractor report; everything ships opt-in until cutover; tests green in CI.

Part of #5894.