* fix(mcp): handle Claude Code GET probe and make stateless_http configurable (#751)
Claude Code v2.1.84+ sends a GET to /mcp/ before POST initialize,
which fails with 405 (stateless) or 400 (stateful). Intercept
sessionless GET requests in MCPMiddleware and return 200 OK so the
client proceeds to POST initialize.
Also make stateless_http configurable via HINDSIGHT_API_MCP_STATELESS
(default: false/stateful) instead of hardcoding true.
Closes#751
* docs: add HINDSIGHT_API_MCP_STATELESS to configuration reference
d8050387e4