fix(tests): replace hardcoded /tmp paths with tempdir + add 300 unit tests (#659)

* test: add unit tests across 20 modules for coverage push

Add 300+ unit tests covering config, context, evaluation, extensions,
LLM, secrets, tools/builder, and tools/mcp modules. All tests are
pure unit tests (no mocks) exercising serde roundtrips, edge cases,
error paths, and business logic.

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

* fix(tests): replace hardcoded /tmp paths with tempfile::tempdir

The e2e_metrics_test::test_metrics_collected_from_tool_trace test was
failing because setup_test_dir() created /tmp/ironclaw_metrics_test but
the fixture referenced /tmp/ironclaw_e2e_test/hello.txt (path mismatch).

Added LlmTrace::replace_paths() to substitute fixture paths at runtime,
then converted all 12 test files from hardcoded /tmp/ironclaw_* paths to
tempfile::tempdir(). Tests are now isolated, parallel-safe, and leave no
debris on disk.

Regression test: test_metrics_collected_from_tool_trace now passes
consistently regardless of prior /tmp state.

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

---------

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

src/setup/wizard.rs

@@ -3258,8 +3258,10 @@ mod tests {
 
     #[tokio::test]
     async fn test_discover_wasm_channels_nonexistent_dir() {
-        let channels =
-            discover_wasm_channels(std::path::Path::new("/tmp/ironclaw_nonexistent_dir")).await;
+        let channels = discover_wasm_channels(
+            &std::env::temp_dir().join("ironclaw_nonexistent_dir_abcxyz123"),
+        )
+        .await;
         assert!(channels.is_empty());
     }