AudioPlayback: add Wi-Fi CLI, platform+network preflight, rootfs check; improve asset logging & exits

- Introduce --ssid/--password (no exports); keep existing flow and names.
- Print platform details via detect_platform, no new files/functions.
- Align with video: rootfs >=2GiB gate, network status/bring-up with NET_STABILIZE_SLEEP and TOP_LEVEL_RUN.
- Before fetching, check for existing clip, log source URL and final size. keep audio_ensure_clip_ready behavior.
- Proper exit codes (PASS/SKIP=0, FAIL=1) multi-line refactors, address ShellCheck SC1091/SC2034 without logic changes.

Signed-off-by: Srikanth Muppandam <[email protected]>

Author: smuppand