Share the Function and MCP tool editor between Agent and Session forms #33

Outcome

Share the Function and HTTP MCP editor primitives used by saved Agent configuration and Session overrides.

Current behavior

AgentForm and SessionToolsEditor contain two similar editors. Both paths are tested and currently work, but duplicated validation and controls can drift as the protocol evolves.

Acceptance criteria

• Extract reusable Function and supported HTTP MCP editor primitives.
• Preserve the saved-Agent rule that unsupported or saved-only tool variants remain visible and cannot be silently removed.
• Preserve the Session-override rule that supported inherited tools can be explicitly replaced or cleared.
• Keep existing serialization, URL/header validation, secret handling, and fail-closed behavior unchanged.
• Retain focused tests for both Agent and Session semantics.

Non-goals

• Advertising tool variants that Core has not exposed.
• Adding browser-side MCP execution.
• Changing Parsar Core.