Add model-based detect_denoise modes

[henryhng]

Summary

Model-based detection denoise modes for ShowDiffraction.

Verification

• Checks run: PYTHONPATH=src pytest -q (13 passed in the denoise test module; parametrized model tests skip when scikit-image/denova are absent)
• User workflow exercised: raw vs anscombe vs denova_tv12 side-by-side Auto pipeline in JupyterLab
• Data: public (Fe3O4 tutorial SAED, pyxem twinned nanowire from Zenodo 15490547)
• Backend and hardware: CPU (devcontainer); denova CUDA/MPS path unverified here
• Load/render/interaction timing: n/a (no frontend changes)
• Evidence artifacts or screenshots: https://henryhg.com/research/denoise-model

Core checklist (every PR)

• The change includes focused tests for Python state/export behavior and
  frontend build coverage where possible; start with PYTHONPATH=src:. pytest -q
  and npm run build, or run scripts/widget_local_signoff.sh.
• Before committing, inspect git status --short and git diff --stat;
  do not commit generated HTML, docs builds, screenshots, local notebooks,
  private data, or machine-specific notes.
• Committed notebooks carry NO baked widget state (metadata.widgets) and
  pass scripts/check_notebook_sizes.py. (No notebook changes in this PR's increment.)
• Only the sections below that this PR touches are kept; the rest are
  deleted from this description.

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This PR workflow follows the packaging standards for reproducible scientific
software described in scikit-package:
S. Lee, C. Myers, A. Yang, T. Zhang, Y. Xiao, and S. J. L. Billinge,
Digital Discovery (2026), DOI
10.1039/d6dd00121a.