feat: add semantic character action ids

[JOY (JOY)]

Summary

• Add CharacterActionId as the gameplay-facing action layer for character visuals.
• Map semantic actions to existing VisualAnimationIntent and shared Animator contract through CharacterAnimationRegistry.
• Update prototype AI, player-agent, NPC chat, and visual hotkey paths to request semantic character actions.
• Document the action registry boundary in architecture, roadmap, and changelog.

Closes #146

Verification

• git diff --check passed.
• npx markdownlint-cli2@0.15.0 CHANGELOG.md ROADMAP.md docs/ARCHITECTURE.md passed.
• Generated-text em dash scan passed for all touched files.
• Local code-review fallback passed manually: no authority, reward, TIME, SECOND, package, provider-key, or model-call boundary changes.
• Unity batch compile for the worktree was attempted with Unity 6000.5.0b9, but a fresh-library Package Manager blocker stopped package resolution before script compile: The "path" argument must be of type string. Received undefined. This matches the existing Unity 6000.5.0b9 blocker tracked in Fix Unity Package Manager path error on 6000.5.0b9 #122. Root MCP compile and Play Mode smoke should run after merge against the warmed active Editor.

Notes

This PR keeps VisualAnimationIntent as the internal animation-layer adapter for existing controller mappings. Gameplay and AI prototype callers should use CharacterActionId going forward.