docs(v0.0.5): comprehensive rustdoc implementation plan (#58)

- Created RUSTDOC_IMPLEMENTATION_PLAN.md in docs/planning/v0.0.5/
- Analyzed current documentation coverage (~25% across crates)
- Defined 4-phase implementation strategy (2-3 weeks, 62 hours)
- Established documentation standards and templates
- Included future enhancements (JSON export for AI integration)
- References attached RUSTDOC_RESEARCH.md for AI integration guidance

Phases:
1. Foundation Setup - Workspace config, CI integration (8h)
2. Compiler Documentation - All compiler crate APIs (27h)
3. Runtime & Godot Docs - Runtime and binding APIs (19h)
4. Validation & CI - Link checking, example testing (8h)

Success criteria: 80%+ coverage, all examples compile, CI enforcement

Author: dev-parkins