U1: Define horror content model and safety copy

[breadback00-dev]

Parent: #16

Purpose

Add case-authored horror content without turning the evidence schema into a general platform.

Scope

• Add a case-level horror layer for escalation phases, safety/intensity copy, unreliable evidence notes, consent prompts, consequence language, and debrief classifications.
• Add content for at least two unreliable evidence moments around the public account and private witness/oracle surfaces.
• Add authoring guidance for evidence variants, consent choices, and debrief endings.
• Add a dedicated psychological-horror playtest doc.

Target files

• Case Box 001 - The Creator Who Left But Kept Posting/src/data/case-001.js
• Case Box 001 - The Creator Who Left But Kept Posting/docs/game-design.md
• Case Box 001 - The Creator Who Left But Kept Posting/docs/case-authoring.md
• Case Box 001 - The Creator Who Left But Kept Posting/docs/psychological-horror-playtest.md

Acceptance checks

• Case loads if horror content is absent.
• Every horror cue references an existing evidence, cast, or custody concept.
• Safety/intensity copy appears before the strongest simulated privacy pressure.
• Docs distinguish stable truth, route responsiveness, and horror presentation.