Converge the test suite: delete dead probes/benches, promote live contracts to the gate

Delete 17 test files (~2500 lines) with no automated entry point: one-off
profiling/bench scripts (cpu-profile, profile-*, *-bench, ab-emitted), stale
smoke probes superseded by real gates (treesitter-smoke, monarch-smoke,
verify-rejects, snapshot), and the token-DFA measurement spike plus its only
consumer (src/token-dfa.ts). Remove src/trace-markers.ts alongside its only
reader (exec-trace).

Gate changes in check.ts:
- drop core/sanity (no-throw only; strictly subsumed by conformance and
  issue-cases) and highlighter/html-lexer-spike (kept as gate:html-lexer
  script; its failures are covered by html-conformance + *-sites gates)
- promote left-recursion, newline-mode, and interpolation-metadata: all
  three carry unique hard assertions for shipped features but previously
  ran only via package scripts or the local verify loop

Harden html-embed-js: the official-grammar boundary comparison was
report-only; now ratchets at 216/221 chars so boundary regressions fail.

44/44 gates pass.

Author: johnsoncodehk