Add MGE point-source (foreground lens) example to multi_gaussian_expansion modeling

[Jammy2211]

What & why

Adds a standalone Lens Point Source section to the imaging MGE modeling example
(scripts/imaging/features/multi_gaussian_expansion/modeling.py), demonstrating how to model a
compact, unresolved point-like component in the foreground lens galaxy (nuclear starburst /
AGN / unresolved bulge) as an MGE Basis.

The section (prose adapted from the mge_point_model_from docstring):

• Explains the compact point-source basis: ~10 linear Gaussians sharing one centre and elliptical
  components, with sigma fixed log-spaced from 0.01″ to 2×pixel-scale (N=4 free params: shared
  centre + shared ellipticity).
• Recreates the Gaussians line-by-line (copy-paste friendly) and attaches the point component
  to the lens galaxy alongside its extended bulge MGE, mass and shear.
• Then shows the al.model_util.mge_point_model_from shortcut producing the identical basis in
  one line.
• Adds the matching __Contents__ entry.

Docs/example only — no library or public-API change.

Scripts Changed

• scripts/imaging/features/multi_gaussian_expansion/modeling.py (+ regenerated
  notebooks/.../modeling.ipynb, llms-full.txt, workspace_index.json)

Notebook regenerated via PyAutoBuild; unrelated pre-existing notebook drift on main was reverted
to keep this PR focused.

Autonomy — --auto safe (docs, small)

Four-leg ship gate:

• Tests: n/a — workspace repo has no pytest suite; no public-API change.
• Smoke: the edited script is not in the curated smoke_tests.txt (not grown to manufacture
  coverage). Validated by running the edited script directly under fast-mode flags
  (PYAUTO_TEST_MODE=2 PYAUTO_SMALL_DATASETS=1 …) → exit 0; new point component appears as
  Basis (N=4) from both the line-by-line and shortcut forms.
• Review: self-review CLEAN — additive example prose + validated composition code, no
  behaviour change.
• Heart: stale-evidence tier — sole reason test-run 2026-07-09 + 58 stale parked scripts
  (organism-scope, unrelated to this branch). Acknowledged by the human at launch.

Autonomous run ends at PR-open. Merge / issue-close remain human acts.

Validation checklist

• Edited script runs end-to-end under fast-mode flags (exit 0)
• point MGE resolves as Basis (N=4) in model.info
• Notebook regenerated; PR scoped to the changed script only
• Human review + merge