Smokes v2 — Minimal Runner and Policy

Policy
- Use [SKIP:<reason>] prefix for environment/host dependent skips.
  - Examples: [SKIP] hakorune not built, [SKIP:env] plugin path missing
  - Keep reasons short and stable to allow grep-based canaries.
- Prefer JSON-only output in CI: set `NYASH_JSON_ONLY=1` to avoid noisy logs.
- Diagnostics lines like `[provider/select:*]` are filtered by default in `lib/test_runner.sh`.

Helpers
- `tools/smokes/v2/lib/mir_canary.sh` provides:
  - `extract_mir_from_output` — between [MIR_BEGIN]/[MIR_END]
  - `assert_has_tokens`, `assert_skip_tag`, `assert_order`, `assert_token_count`
- `tools/lib/canary.sh` provides minimal, harness-agnostic aliases:
  - `extract_mir_between_tags` — same as `extract_mir_from_output`
  - `require_tokens token...` — fail if any token missing

Notes
- Avoid running heavy integration smokes in CI by default. Use `--profile quick`.
- When a test depends on external tools (e.g., LLVM), prefer `[SKIP:<reason>]` over failure.

Quick tips
- EXE-heavy cases (e.g., `phase2100/*`) may take longer. When running quick with these tests, pass a larger timeout like `--timeout 120`.
- Smokes v2 auto-cleans temporary crate EXE objects created under `/tmp` (pattern: `ny_crate_backend_exe_*.o`) after the run.