Fix canvas context state leakage in neon and render pipeline

[serzel]

Motivation

• Eliminate canvas rendering state leaks that cause non-neon drawing (shots, particles) to inherit neon glow properties such as shadowBlur, shadowColor, globalAlpha, or altered globalCompositeOperation.
• Make neon UI drawing functions robust and self-contained so they never rely on external context state and cannot corrupt the shared CanvasRenderingContext2D.

Description

• Refactored src/ui/neon.js to wrap all drawing passes with withIsolatedContext(ctx, ...) and added resetGlowState(ctx) to explicitly normalize globalAlpha, globalCompositeOperation, shadowColor, and shadowBlur before use and on exit.
• Replaced any implicit intensity multiplication and clamped intensity usage to safe bounds and removed reliance on *= style operations for globalAlpha across neon strokes.
• Reworked src/engine/Game.js render pipeline into isolated stages: #drawGame(), #drawParticles(), and #drawShots() that each use ctx.save()/ctx.restore() with try/finally and explicitly reset glow-sensitive state after each stage.
• Wrapped HUD rendering and drawHUD() body in protected save()/restore() blocks with explicit state cleanup in src/ui/HUD.js to prevent HUD or neon draws leaking into subsequent profiler/overlay passes.

Testing

• Ran syntax checks: node --check src/ui/neon.js && node --check src/engine/Game.js && node --check src/ui/HUD.js, which completed successfully.
• Started a static server and attempted a Playwright-based page load + screenshot to visually validate rendering, but the browser navigation in this environment failed with net::ERR_EMPTY_RESPONSE (visual validation not captured).

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Codex Task