docs(roadmap): add integration test plan for future PRs

Save detailed integration test coverage plan to
.claude/plans/integration-tests.md covering insta snapshot tests,
temp-env config testing, wiremock SSE streaming, and logic extraction.
Add test coverage section to roadmap under Current Focus.

Author: hakula139

docs/roadmap.md

@@ -58,6 +58,11 @@ The project direction is simple:
 
 - Viewport virtualization for long conversations.
 
+### Test Coverage
+
+- Integration test infrastructure — `insta` snapshot tests for TUI render methods, `temp-env` for config env var testing, `wiremock` for Anthropic SSE streaming client. See `.claude/plans/integration-tests.md`.
+- Logic extraction for testability — pure reducers from `app.rs`, key interpretation from `input.rs`, config merge from `config.rs`.
+
 ### Tool & Prompt Enhancements
 
 - Centralized output truncation — move truncation from individual tools into the tool dispatch layer. Enables consistent behavior and large-output persistence to disk.