feat: real gunshots, localized 3D audio, seamless music, better animations

Audio:
- All ballistic weapons now fire real firearm recordings (The Free Firearm
  Sound Library, CC0): AK-47 uses actual AK-47 shots, M4=AR-15, MP7=PPSh,
  AWP=Mosin Nagant, DMR=Savage 10, shotgun=Mossberg/Nova, nailgun=Ruger .22,
  rocket/mortar layered with real booms. Plasma keeps its energy sound.
- Reload is real lever-action foley instead of interface clicks
- Projectile flight loops localized: unit_size 50->6, max_db 6->0,
  max_distance 45 — no more mortar/rocket drone in every player's ear;
  loops also got proper loop_end (was a zero-length loop)
- Flight loops lowpassed into soft whooshes instead of sci-fi engine drones
- Menu music converted to OGG with native full-track looping (47s seamless,
  replaces the broken manual WAV loop points)

Animations (movement-shooter pass):
- Rebaked miku.glb with 4 new clips from the CC0 library: Grapple (swim
  reach — reads as a swing), PistolIdle (armed idle with weapon up),
  PistolShoot, PistolReload
- Armed idle: standing with a weapon now uses PistolIdle instead of
  arms-at-sides
- Slide pose overhaul: legs kick out front (lead/trail thighs, knees
  straighten) — feet-first slide instead of "sitting in a crouch"
- Wall run: forward drive pitch + inner arm reaches out to the wall
- Per-transition blend times: dash/hit/jump cut fast (0.05-0.08s),
  locomotion cross-fades smoothly (0.2-0.25s); CrouchWalk speed-scales

Fixes:
- Third-person camera no longer renders the first-person viewmodel layer
  (the gun/arms floated in front of the third-person view)

Verified: 11/11 movement tests, smoke test 0 failures (17 clips resolved),
third-person run screenshot shows grounded animated model, no floating gun.

Co-Authored-By: Claude Fable 5 <[email protected]>

assets/sounds/SOURCES.md

@@ -3,6 +3,11 @@
 All current WAVs are forged (pitch/layer/trim via ffmpeg — see repo history)
 from these CC0 packs, no attribution required:
 
+- The Free Firearm Sound Library (Ben Jaszczak et al.) — CC0,
+  https://opengameart.org/content/the-free-firearm-sound-library
+  → all ballistic weapon fire sounds (AK-47/AR-15/PPSh/Mosin/Savage/
+  Mossberg/Nova/Ruger/Carl Gustav recordings) + reload (Model 1894 lever)
+
 - Kenney Impact Sounds — https://kenney.nl/assets/impact-sounds (CC0)
 - Kenney Sci-Fi Sounds — https://kenney.nl/assets/sci-fi-sounds (CC0)
 - Kenney Interface Sounds — https://kenney.nl/assets/interface-sounds (CC0)