cleanup: fix all build warnings, delete dead DMN context code
- Delete poc-daemon/src/context.rs dead code (git_context, work_state,
irc_digest, recent_commits, uncommitted_files) — replaced by
where-am-i.md and memory graph
- Remove unused imports (BufWriter, Context, similarity)
- Prefix unused variables (_store, _avg_cc, _episodic_ratio, _message)
- #[allow(dead_code)] on public API surface that's not yet wired
(Message::assistant, ConversationLog::message_count/read_all,
Config::context_message, ContextInfo fields)
- Fix to_capnp macro dead_code warning
- Rename _rewrite_store_DISABLED to snake_case
Only remaining warnings are in generated capnp code (can't fix).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>