add cdoc — Claude Code diagnostics and session health monitoring

[Moguifeng-9119]

I built cdoc after getting tired of realizing halfway through a session
that Claude Code had silently dropped instructions from my CLAUDE.md.
It reads the JSONL session logs that Claude Code already writes to disk
and runs seven health signals against them — no network calls, no API
access, no setup.

It also does basic config auditing: what rules/skills/agents/hooks you
have installed, whether cross-references are broken, whether settings
are valid.

Written in Rust. Binaries on the releases page, cargo install works,
crates.io coming shortly.