Root cause: compile-and-eval for def created Janet global but never
interned the var in Jolt's namespace. Bare symbols fell through to
interpreter which couldn't find them.
Fixes:
- eval-string: bare symbols and tuples now go through compile path
- compile-and-eval: def/defn/defn- forms intern result in Jolt namespace
- New tests: defn/def integration (4 assertions)
All 317 tests pass.
