feat: consume @jambonz/schema ^0.4.0 — llm optional, no vendor enum

[davehorton]

What

Updates the SDK to @jambonz/schema@^0.4.0 and reconciles the TS types with the current schema.

• llm is now optional on the agent verb, and llm.vendor/llm.model are optional within it — matching schema 0.4.0. When omitted, the server resolves them from the application's default LLM (exactly like stt/tts). AgentVerb.llm, AgentLlm.vendor, and AgentLlm.model are now optional.
• Retires the llm.vendor enum codegen. The schema intentionally has no vendor enum (so new LLMs don't require a schema release), so scripts/gen-llm-vendors.mjs and the generated LLM_VENDORS/LlmVendor union are removed. LlmVendor is now a free-form string; vendor is validated at runtime by the server against its registered @jambonz/llm adapters. Removed the gen:types/prebuild/pretypecheck scripts and the schema-drift test that guarded the union.
• Schema-drift catch-up (needed to pass the drift tests after the bump): added dial.srtpEncryption and recognizer.xaiOptions, which landed in the schema between 0.3.19 and 0.4.0.

Breaking change

LLM_VENDORS (the exported vendor array) is removed, and LlmVendor widens from a union to string. Consumers relying on the union for exhaustiveness will need to adjust. Suggest a minor bump given 0.x.

Tests

npm test — 122 pass. Typecheck clean. Build (tsup) clean. The removed test was the LLM_VENDORS equals agent.schema.json llm.vendor.enum drift check, which no longer applies.