[vshalpnjabi]

Summary

list_label now rejects perPage values outside 1..100 instead of passing 0 through.

Why

The advertised schema says minimum: 1, but the runtime input schema doesn't enforce it, so perPage: 0 reached the handler and was silently replaced with the default page size.
Fixes #3647

What changed

• listLabelsLegacy reads perPage only when it's present and returns perPage must be between 1 and 100, got N when it's out of range. The default still applies when it's omitted.
• Added a table case for perPage: 0 and updated the >100 case to the new message.
• Added TestListLabelPerPageZeroThroughToolCall, which calls the registered tool through an MCP session and asserts the error and that no GraphQL request is made. It fails on main.

MCP impact

• Tool schema or behavior changed
  list_label returns a tool error for perPage 0 or below, matching the schema it already advertises. The schema is unchanged.

Prompts tested (tool changes only)

• Not tested with a live client. Covered by the tool-call test above.

Security / limits

• No security or limits impact

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Also ran go test -v ./..., UPDATE_TOOLSNAPS=true go test ./... (no snapshot changes) and script/generate-docs (no diff).

Docs

• Not needed