Add max LLM calls to server commands

[sylvesterkaczmarek]

Closes #5434

Summary

• Adds --max_llm_calls to adk web and adk api_server.
• Passes explicit values through get_fast_api_app and ApiServer.
• Applies the limit to /run, /run_sse and /run_live.
• Leaves the option unset by default so ADK_MAX_LLM_CALLS and the existing RunConfig default still work.
• Adds CLI parsing, forwarding and live-run propagation tests.

Validation

• CLI/FastAPI suites → 243 passed, 5 skipped, 2 xfailed
• CLI option/signature suite → 8 passed
• Pre-commit checks on all changed files → passed

A remote model endpoint was not used.