refactor: co-locate sys tool handlers and extract savePayload to payload.go

[Copilot]

Two semantic placement issues identified in a codebase analysis: sysInitHandler lived in session.go instead of alongside the other sys tool handlers, and savePayload was embedded in the 815-line jqschema.go despite being a self-contained concern.

internal/server/

• Moved sysInitHandler from session.go → system_tools.go, so all sys___* handlers registered in registerSysTools() are now co-located
• Removed unused sdk import from session.go
• session.go now focuses purely on session lifecycle

internal/middleware/

• Extracted savePayload from jqschema.go → new payload.go, following the existing schema.go split-by-responsibility pattern
• Removed unused os and path/filepath imports from jqschema.go
• jqschema.go drops ~57 lines; payload storage is independently locatable and testable

[Copilot]

Pull request overview

This PR is a refactor to improve code organization in the MCP Gateway by co-locating system tool handlers and splitting payload persistence into a dedicated middleware file, keeping session lifecycle and jq-schema responsibilities more focused.

Changes:

• Moved sysInitHandler from session.go to system_tools.go to co-locate all sys___* handlers with sys tool registration.
• Extracted savePayload from jqschema.go into a new payload.go file in internal/middleware/.
• Cleaned up now-unused imports in session.go and jqschema.go.

Show a summary per file

File	Description
internal/server/system_tools.go	Adds sysInitHandler alongside other sys tool handlers.
internal/server/session.go	Removes sysInitHandler and drops the unused SDK import, keeping the file focused on session lifecycle helpers.
internal/middleware/payload.go	New file containing savePayload for payload-on-disk handling.
internal/middleware/jqschema.go	Removes inline savePayload and associated imports after extraction.

Copilot's findings

Tip

Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

• Files reviewed: 4/4 changed files
• Comments generated: 2