refactor(llm): split claude.rs (5,206 lines) into submodules #1965
Description
Summary
Split crates/zeph-llm/src/claude.rs (5,206 lines) into dedicated submodules.
Target structure
claude/
mod.rs — ClaudeProvider struct, trait impl, public API (~1200 lines)
request.rs — request building, system block splitting, message conversion (~1500 lines)
response.rs — response parsing, SSE, thinking block handling (~1000 lines)
cache.rs — prompt cache utilities, block markers (~500 lines)
tests.rs — unit tests extracted from mod.rs (~1000 lines)
Acceptance criteria
- No file exceeds 2,000 lines
- All existing tests pass unchanged
- LLM serialization gate: live Claude API session with tool use and cache hits, no 400/422 errors
Part of EPIC-04