mcp-context-budget v0.4.0

• Release the post-v0.3.0 JSON-lines / Content-Length stdio framing compat for
  --allow-start introspection. allow-start-demo now prints
  STDIO_FRAMING_*=PASS proof lines without changing the transport
  implementation.
• Parallelize Ollama embeddings in semantic-select via bounded stdlib
  ThreadPoolExecutor batching when --embedding-backend ollama is selected.
  prove-parallel-ollama-demo prints PARALLEL_OLLAMA_BATCHED=true;
  semantic-demo with fixture backend prints SEMANTIC_SELECT_STATUS=PASS.
• Defer live-response-compression and broader CLI polish to v0.5.
• Post-review-pipeline hardening folded into this release: fast fail-closed
  shutdown (cancel_futures) + bounded in-flight window for the parallel Ollama
  path, fixture-only semantic-demo, matched stdio-framing fixture mode, and an
  observable (non-traceback) prove_stdio_framing failure path.

Full changelog: see CHANGELOG.md 0.4.0.