fix(core): enforce maxSteps limit exactly

[cosin2077]

What

Fix an off-by-one error in PageAgentCore.execute() that allows one extra agent step beyond maxSteps.

maxSteps is documented as the maximum number of steps a task may take, but the loop currently increments step and only stops when step > maxSteps. As a result, maxSteps: 1 can execute two LLM/tool steps, and the default maxSteps: 40 can execute 41.

This changes the boundary check to stop when step >= maxSteps and adds a regression test that verifies maxSteps: 1 performs exactly one LLM invocation before returning the step-limit error.

Type

• Bug fix
• Feature / Improvement
• Refactor / Chores
• Documentation / Website / Demo / Testing
• Breaking change

Testing

• npm test -w @page-agent/core
• npm run typecheck
• npm run lint

The patch was reviewed against current main (632424b).

Requirements / 要求

• I have read and follow the Code of Conduct and Contributing Guide.
• I have personally reviewed and meaningfully authored/reviewed every change before submission.