fix: enforce JSON-API headers via httpx event hook

[sylvainkalache]

Summary

• Fixes HTTP 415 (Unsupported Media Type) errors on all API calls when running with newer fastmcp versions (>=2.10)
• Root cause: newer fastmcp calls client.send() instead of client.request(), bypassing our header override. The __getattr__ delegation silently forwarded send() to the inner httpx client without applying Content-Type: application/vnd.api+json
• Adds an httpx event hook (_enforce_jsonapi_headers) that enforces correct headers at the transport level before every outgoing request, regardless of how it was initiated
• Adds explicit send() proxy and fixes base_url property for newer fastmcp compatibility

Test plan

• All 244 existing tests pass
• Deploy and verify listTeams, getCurrentUser, and other tools no longer return 415
• Verify hosted mode with MCP client (Claude Desktop / Claude Code)

[greptile-apps]

Greptile Overview

Greptile Summary

• Moves JSON:API header enforcement from a client.request() override to an httpx request event hook so headers apply even when client.send() is used (newer fastmcp behavior).
• Adds explicit send() proxy and adjusts base_url property handling for compatibility with newer fastmcp/httpx client usage.
• Updates uv.lock to reflect dependency/lock changes related to the httpx/fastmcp compatibility fix.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk.
• Changes are tightly scoped to httpx request header enforcement and compatibility with newer fastmcp calling patterns, and do not introduce new control flow outside the client wrapper. No definite runtime errors or security regressions were identified in the modified code.
• No files require special attention

Important Files Changed

Filename	Overview
src/rootly_mcp_server/server.py	Adds an httpx request event hook to enforce JSON:API headers on every outgoing request, plus explicit send() proxy and base_url handling for newer fastmcp behavior; no correctness issues found in the changes.
uv.lock	Lockfile updated to align dependency resolution with the header enforcement changes; no code-level issues to address.