docs: expand READMEs for stockflow, control, games, and examples

[rororowyourboat]

Summary

• gds-stockflow README expanded from 3 → 239 lines: quick start, element docs, semantic type system, verification checks, architecture
• gds-control README expanded from 5 → 268 lines: quick start, state-space mapping, element docs, semantic types, verification checks, Mermaid diagram
• gds-games README expanded from 88 → 430 lines: game type docs, dual IR explanation, verification tables, v0.3.0 APIs (FeedbackFlow, parallel(), multi_agent_composition(), Pattern.specialize(), discover_patterns())
• gds-examples README updated: fixed directory paths to stockflow//control//games/, added domain DSL cross-references, added domain column to learning path

Test plan

• Verify all package READMEs render correctly on GitHub (Mermaid diagrams, tables, code blocks)
• Confirm Quick Start code examples are accurate against current APIs
• Check all cross-links resolve to correct targets

🤖 Generated with Claude Code