fix: Move streamable HTTP transport from /mcp to root /

[Copilot]

• Update Routes.MCP = '/mcp' to '/' in src/actor/const.ts; remove now-redundant Routes.ROOT
• In src/actor/server.ts: remove old GET / info-response handler; remove GET Routes.MCP (405) handler per review; replace Routes.ROOT with Routes.MCP in HEAD handler; remove unused HEADER_READINESS_PROBE and getActorRunData imports
• Update DEVELOPMENT.md: replace /mcp?ui=openai with /?ui=openai in all endpoint references
• Revert MCP_STREAMABLE_ENDPOINT in src/const.ts back to '/mcp' — this constant is used for third-party Actor endpoint discovery, not our own server routing
• Lint clean, all 402 unit tests pass

Original prompt

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This section details on the original issue you should resolve

<issue_title>Dev server - ,ove streamable transport from /mcp to root /</issue_title>
<issue_description>In src/actor/server.ts we serve streamable transport from the /mcp route.

At root / we return 200. The reason is historical, as this file was used as an Actor.

Going forward, we should serve streamable transport directly from root to remove confusion for different setups (for staging and production, streamable transport is directly at root).

Note that src/server_card.ts already declares endpoint: '/', so the server card is already inconsistent with the actual /mcp route. Moving to root aligns them.

• Move POST /mcp, GET /mcp, DELETE /mcp handlers to POST /, GET /, DELETE /
• Update MCP_STREAMABLE_ENDPOINT = '/mcp' in src/const.ts
• Update getHelpMessage in src/actor/const.ts which references /mcp</issue_description>

<agent_instructions>Keep the solution minimal, do not put anything extra, do not remove comments etc</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Dev server - move streamable transport from /mcp to root / #528

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[jirispilka]

@copilot you need to update CLAUDE.md or DEVELOPMENT.md with this change so that developers are aware of that!

[Copilot]

@copilot you need to update CLAUDE.md or DEVELOPMENT.md with this change so that developers are aware of that!

Done in fa1a4f2 — updated all /mcp?ui=openai endpoint references in DEVELOPMENT.md to /?ui=openai.

[jirispilka]

@copilot buddy, you have changed MCP_STREAMABLE_ENDPOINT that is used for a different purpose and changing this will break other parts of code.

Let's fix it, please think before you do changes

[Copilot]

@copilot buddy, you have changed MCP_STREAMABLE_ENDPOINT that is used for a different purpose and changing this will break other parts of code.

Let's fix it, please think before you do changes

Fixed in f9cdd4a — reverted MCP_STREAMABLE_ENDPOINT in src/const.ts back to '/mcp'. That constant is used by src/mcp/actors.ts for third-party Actor endpoint discovery, not for our dev server routing (which is controlled by Routes.MCP in src/actor/const.ts).

[jirispilka]

Looks good now, but it took more turn around than necessary