Fix Google Photos uploads and MCP HEAD responses

[saga-agent]

Summary

• send generated Google Photos raw uploads to /v1/uploads instead of the invalid /uploads path
• preserve WHATWG response status and headers when wrapping MCP responses for Effect HTTP
• reject HEAD on bare, org-scoped, and toolkit MCP routes with 405 application/json before the SPA fallback can turn it into 200 application/octet-stream
• add focused regression coverage for both fixes
• add a patch changeset for @executor-js/plugin-openapi

Root cause

HttpServerResponse.raw(response) preserved the nested web Response for ordinary requests, but Effect strips the body for HEAD and serializes the outer wrapper. Because the outer wrapper did not copy the nested status and headers, the result became an empty 200 without an MCP content type; nginx surfaced that as application/octet-stream.

Verification

• bun run --cwd packages/plugins/openapi test -- src/providers/google/discovery.test.ts (10 passed)
• bun run --cwd packages/hosts/mcp test (65 passed)
• bun run --cwd apps/host-selfhost test -- src/mcp/org-path.test.ts src/mcp/mcp.test.ts (10 passed)
• bun run --cwd packages/hosts/mcp typecheck
• bun run --cwd apps/host-selfhost typecheck
• focused oxfmt --check and git diff --check
• real Bun server smoke: HEAD /mcp, HEAD /default/mcp, and HEAD /mcp/toolkits/deploy each returned 405 Method Not Allowed with Content-Type: application/json; HEAD / remained 200 text/html

The complete self-host test command was also attempted, but its existing long-lived daemon test did not exit, so it is not represented as a passing check here.