fix: exclude custom-harness packages from nextest, run them with cargo test

cargo-nextest can't discover tests in packages with `harness = false`
(e2e_snapshots, plan_snapshots) because they output custom formats
instead of the standard libtest listing. Split the musl test run:
- nextest for standard-harness tests (parallel, per-process isolation)
- cargo test for custom-harness packages (already run sequentially)

https://claude.ai/code/session_011H8UR3gS6hoyQAf2x7Dfw8

Author: claude

.github/workflows/ci.yml

@@ -175,8 +175,11 @@ jobs:
       # Use cargo-nextest: it runs each test in its own process, avoiding
       # musl's fork()-in-multithreaded-process SIGSEGV while keeping parallel
       # execution (across processes instead of threads within one process).
+      # Exclude packages with custom test harnesses (harness = false) since
+      # nextest can't discover their tests; run those with cargo test instead.
       - run: cargo install cargo-nextest --locked
-      - run: cargo nextest run
+      - run: cargo nextest run --workspace --exclude vite_task_bin --exclude vite_task_plan
+      - run: cargo test -p vite_task_bin -p vite_task_plan
 
   fmt:
     name: Format and Check Deps