docs: correct MCP transport (SSE to streamable HTTP) and Claude Desktop config path

[jaymeklein]

What changed

Corrects the MCP transport description in the README, which still called it SSE in three places even though the server runs stateless streamable HTTP (api/services/mcp/server.py — it deliberately abandoned SSE because the stream died on uvicorn --reload). The README's own MCP section already said "streamable HTTP," so the three stale references were internally inconsistent with both the code and the rest of the doc.

README.md

• Features bullet — "MCP server over SSE" → "over streamable HTTP"
• Architecture diagram — REST + MCP/SSE → REST + MCP/HTTP
• Ports table — REST + MCP/SSE → REST + MCP/HTTP
• Claude Desktop config path — corrected from the Linux-style ~/.config/claude/… to the macOS location ~/Library/Application Support/Claude/claude_desktop_config.json, with an explicit macOS / Windows split

api/main.py and api/routers/mcp.py

• Updated two stale "SSE" code comments to "streamable-HTTP" so the comments match the transport actually mounted.

Why

Documentation-accuracy follow-up. A reader wiring up an MCP client would otherwise get contradictory signals about the transport, and the macOS config path pointed at a directory Claude Desktop does not use.

Reviewer notes

• Docs + comment-only change — no runtime behavior changes. Verified against the code (FastMCP(..., stateless_http=True, json_response=True) in api/services/mcp/server.py).
• While reviewing, I also confirmed the README's other claims are accurate and left them untouched: default ports, the MCP tool list/signatures, the 60 rpm rate limit, the presigned-URL 1 h expiry, the MinIO/GPU compose commands, and http://localhost:8000/docs (returns 200 on the live stack).
• ruff passes on the two edited Python files; mypy/pytest are not meaningful for comment-only edits.
• This branch was previously merged via docs(claude): lean CLAUDE.md index + path-scoped rules, and a standards-check skill #73; origin/main..HEAD is exactly this one commit, so the PR diff is just these fixes.