Improve platforming feel, add player health/respawn, enemy chase AI, rooms 2–4, and HUD rebuild

[Copilot]

Adds coyote time, jump buffering, wall-jump improvements, a full player health/iframes/knockback/death-respawn cycle, enemy patrol→chase AI with stomp kills, three new rooms wired into the room chain, and a rebuilt HUD with health, level name, and respawn overlay.

Platforming (Player.gd)

• floor_snap_length = 6.0 — step-up collision fix
• Coyote time (0.12 s) and jump buffering (0.12 s pre-press queued for next landing)
• Wall-jump lock (0.25 s) prevents immediate re-stick; plays "jump" animation instantly
• Air acceleration raised 25% → 40% of ground accel

Player health system (Player.gd, GameState.gd)

• GameState gains health_changed(current, max), player_died, player_respawned signals; player_stamina now has an emitting setter
• take_damage(amount, knockback_dir) — applies knockback velocity, starts 1.2 s iframes (blinking sprite)
• instant_kill() — bypasses iframes; used by death pits
• stomp_bounce() — upward reward for stomping enemies
• DEAD state: 2 s pulsing-red death animation → respawn at spawn position with full HP and iframes

Enemy AI (Enemy.gd, Enemy.tscn)

• Exports: chase_speed, detect_range, max_health
• Switches patrol → chase when player enters detect_range
• Stomp detection: player falling (velocity.y > 50) from above → enemy.take_damage(1) + player.stomp_bounce(); otherwise deals player.take_damage(1, dir)
• ♥ health label above each enemy, updated on hit

DeathArea (DeathArea.gd)

• Calls player.instant_kill() instead of hard-reloading the scene directly

HUD (HUD.gd, HUD.tscn)

• Level name label (get_parent().name)
• Health row: filled/empty hearts — "♥".repeat(hp) + "♡".repeat(max - hp)
• Full-screen respawn overlay (ColorRect + label), shown on player_died, hidden on player_respawned

New rooms + wiring

Room	Difficulty notes	Loop
Room2	3 enemies (one 2 HP), moving platforms	Room1 → Room2 → Room3
Room3	4 enemies (two 2 HP), wall-jump gaps	Room2 → Room3 → Room4
Room4	Gauntlet: 4 enemies (three 2 HP + one 3 HP)	Room4 → Room0

Room1 gains a right-side RoomWarpForward completing the full loop.

Original prompt

Pull request: #3

Improve platforming: fixed collision stepping, added coyote time + jump buffering, tuned air acceleration, and update wall-jump behavior/animations.
Add player health, invincibility frames, knockback, and a death/respawn animation loop; introduce enemy patrol/chase AI with health and indicators.
Add new rooms (rm_2–rm_4) plus warp wiring, and rebuild HUD elements (health/timer/diamonds/level name/respawn overlay).

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