fix: Deep readability polish — detailed concept explanations across all sections

- Expand async generator, EventEmitter, callback pattern comparisons (§3.1)
- Add concrete examples for atomic state, StreamingToolExecutor concurrency (§3.2-3.3)
- Full cache edit block pinning explanation with 5-step mechanism (§4.2)
- Expand Context Collapse preview/commit model with DB view analogy (§4.3)
- Add circuit breaker motivation and 13K buffer rationale (§4.4)
- Explain ToolUseContext as "world object", DeepImmutable vs Readonly (§5.1)
- Cache breakpoint and tool pool sorting explained step by step (§5.3)
- Security layers: add threat scenarios, categorize DANGEROUS_BASH_PATTERNS (§6)
- Explain teammate, peer, SyntheticOutput, recursive execution guard (§7)
- Translate remaining English code comments to Korean
- Sync all improvements to English post

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bits-bytes-nn