chore: remove dead code (#648) (#703)

* chore: remove dead code (LlmEvaluator, chunk_by_paragraphs, bundled channel installer, Reasoning::safety)

Delete unused code flagged in #648:
- evaluation/success.rs: delete LlmEvaluator struct/impl, remove #[allow(dead_code)] from RuleBasedEvaluator methods
- workspace/chunker.rs: delete chunk_by_paragraphs() and its tests (zero production callers)
- extensions/manager.rs: delete install_bundled_channel_from_artifacts() (hot-activation never shipped)
- llm/reasoning.rs: remove unused safety field from Reasoning struct; cascade removal through ContextCompactor, HeartbeatRunner, LlmSoftwareBuilder, and all callers

Closes #648

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: move RuleBasedEvaluator into test module to fix dead_code warning

RuleBasedEvaluator has no production callers -- it was only used in
tests of itself. Moving it into #[cfg(test)] eliminates the clippy
dead_code error that broke CI.

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

src/agent/agent_loop.rs

@@ -417,7 +417,6 @@ impl Agent {
                         hygiene,
                         workspace.clone(),
                         self.cheap_llm().clone(),
-                        self.safety().clone(),
                         Some(notify_tx),
                         self.store().map(Arc::clone),
                     ))