feat: add point-source imaging simulator

[Jammy2211]

Summary

• add a documented imaging simulator for ag.lp.PointSource
• demonstrate sub-pixel placement with a PSF sampled at twice the detector resolution
• describe the total-flux convention and the ag.lp_linear.PointSource fitting counterpart
• generate the matching notebook and workspace catalogue entries

Scripts Changed

• scripts/imaging/features/point_source/simulator.py
• notebooks/imaging/features/point_source/simulator.ipynb
• smoke_tests.txt
• generated llms-full.txt and workspace_index.json

Upstream PR

PyAutoLabs/PyAutoGalaxy#562

Test Plan

• Run the simulator directly against the upstream feature branch
• Validate the generated notebook with nbformat
• Run Black and workspace size checks
• Run all 14 user-workspace Python smoke entries
• Confirm GitHub Actions Smoke Tests and Navigator Check

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