feat(player): improve jump feel with apex assist and ledge catch

[h2cone]

Summary

Improves player movement feel and reliability around jumps and walls:

• Jump apex assist — gravity is reduced and turn acceleration is boosted near the jump apex for tighter air control.
• Jump buffering while falling — presses during a fall arm the buffer so the landing jump registers.
• Landing turn grace — a short window after landing lets the player reverse direction without a turn-accel penalty.
• Ledge catching — falling against a wall now snaps onto nearby ledges instead of sliding past them.
• Head-bonk correction — bumping a ceiling while hugging a wall restores upward velocity after the corner correction nudge.
• Updates the gdext revision and regenerates the LDtk room scenes (scene serialization only; no level design changes).

Verification

• cargo test --locked — 120 passed, 0 failed
• cargo fmt --check — clean

Screenshots

To be added after gameplay pass.