Define milestones for ge-hch (Dynamic Interactive Story Engine)

[SorraTheOrc]

This PR creates milestone epic children for ge-hch (Dynamic Interactive Story Engine) and chains their dependencies.

Included child epics (milestones):

• ge-hch.2 — M0 — Scaffold / Smoke Demo
• ge-hch.3 — M1 — MVP: Ink runtime + UI + save/load + telemetry + demo story
• ge-hch.4 — M1.5 — Content iteration tooling & replay regression
• ge-hch.5 — M2 — AI-assisted branching integration
• ge-hch.6 — M3 — Basic staging (backgrounds & posed characters)
• ge-hch.7 — M4 — Reactive simulated world & state model
• ge-hch.8 — M5 — Systemic NPCs and narrative director (optional)

Notes:

• Created on branch milestones-ge-hch/milestones. bd changes (.beads/issues.jsonl) were committed.
• I did not modify other local edits (.opencode/*).