U6: Add sensory corruption, micro-audio, and intensity controls

[breadback00-dev]

Parent: #16

Purpose

Give the horror layer felt texture while preserving usability and player control.

Scope

• Add phase classes for subtle palette cooling, text shimmer, timestamp jitter, and evidence-card pulse.
• Use CSS variables and existing component patterns to avoid layout shifts and unreadable text.
• Add reduce-intensity and mute controls near existing reset/reference controls.
• Implement micro-audio only after a user gesture.
• Respect prefers-reduced-motion and disable motion-heavy effects under reduced intensity.

Target files

• Case Box 001 - The Creator Who Left But Kept Posting/index.html
• Case Box 001 - The Creator Who Left But Kept Posting/src/scripts/app.js
• Case Box 001 - The Creator Who Left But Kept Posting/src/scripts/sensory-engine.js
• Case Box 001 - The Creator Who Left But Kept Posting/src/styles/base.css
• Case Box 001 - The Creator Who Left But Kept Posting/src/styles/layout.css
• Case Box 001 - The Creator Who Left But Kept Posting/src/styles/components.css
• Case Box 001 - The Creator Who Left But Kept Posting/tests/horror-engine.test.js
• Case Box 001 - The Creator Who Left But Kept Posting/tests/sensory-engine.test.js
• Case Box 001 - The Creator Who Left But Kept Posting/docs/psychological-horror-playtest.md

Acceptance checks

• Audio never starts before a user gesture.
• Mute stops current and future audio cues.
• Reduced intensity removes motion-heavy effects while keeping state readable.
• Sensory helpers map muted/reduced states to no-audio/low-motion presentation.
• Desktop and 390px mobile layouts have no overlapping text after corruption classes are active.
• Evidence, reconstruction, custody, and modals remain keyboard usable.