audio: add Proof-of-Antiquity hardware cue set

[eldwin-easynet-world]

Summary

• Adds five original Proof-of-Antiquity / hardware-state cue sounds under pk3_build/sound/antiquity/rustchain/.
• Adds a deterministic procedural generator so the assets can be regenerated without samples, recordings, speech models, or external media.
• Adds focused tests covering cue inventory, OGG/Vorbis packaging, mono 48 kHz metadata, duration, peak level, and audible RMS.

Cue set

• crt_boot_nonce.ogg - vintage node boot / nonce accepted
• power8_validator_spin.ogg - POWER8/server-class validator spin-up
• g4_cube_sync.ogg - G4-style node sync / join cue
• antiquity_weight_boost.ogg - antiquity multiplier / bonus cue
• vm_rejected_flatline.ogg - VM/emulator fingerprint rejection

Bounty context: Scottcjn/rustchain-bounties#293.

Validation

• /tmp/xonotic-audio-venv/bin/python tools/audio/generate_rustchain_antiquity_cues.py
• /tmp/xonotic-audio-venv/bin/python -B -m py_compile tools/audio/generate_rustchain_antiquity_cues.py tests/test_antiquity_cue_sounds.py
• /tmp/xonotic-audio-venv/bin/python -B -m unittest tests.test_antiquity_cue_sounds tests.test_music_loop tests.test_stinger_sounds tests.test_announcer_sounds -v - 19 tests OK
• git diff --check