docs: fix dead internal references (hygiene refs tier) - #56

The hygiene `refs` tier found 18 dead internal references in this
tutorial series' prose — sibling-workspace paths that moved, plus a few
references that were copied in unqualified from another repo.

- `simulators/start_here.ipynb` (x5) ->
  `autolens_workspace/*/imaging/simulator.ipynb`, the script literally
  titled "Simulator: Start Here" (this repo's folder is `simulator/` and
  has no start_here of its own)
- `autolens_workspace/*/guides/over_sampling.ipynb` ->
  `guides/advanced/over_sampling.ipynb`
- `imaging/log_likelihood_function/parametric.ipynb` ->
  `imaging/likelihood_function.ipynb`
- `imaging/log_likelihood_function/inversion.ipynb` ->
  `imaging/features/pixelization/likelihood_function.ipynb`
- `modeling/features/multi_gaussian_expansion.py` ->
  `imaging/features/multi_gaussian_expansion/modeling.py`
- `modeling/features/shapelets.py` ->
  `imaging/features/advanced/shapelets/modeling.py`
- `imaging/features/pixelizations/modeling.py` -> `pixelization/` (singular)
- `notebooks/modeling/features/no_lens_light.ipynb` ->
  `notebooks/imaging/features/no_lens_light/modeling.ipynb`
- `howtolens/chapter_optional/tutorial_searches.ipynb` -> the repo-local
  `chapter_optional/tutorial_searches.ipynb`
- the two unqualified `imaging/features/pixelization/{modeling,fit}.py`
  references in the no-lens-light simulator name the autolens_workspace
  scripts that actually consume the `mask_extra_galaxies.fits` it writes
- tutorial 2's "run as standalone scripts" note pointed at HowToGalaxy
  paths under autolens_workspace; it now mirrors HowToGalaxy's own
  corrected wording and names this repo's chapter 2 script

The two remaining `autolens_workspace/dataset/imaging/howtolens/`
references are left as-is: that folder is written at runtime by
`tutorial_6_data.py`, so its absence from a checkout proves nothing.

Notebooks and the navigator catalogue regenerated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PzN9PZfG5zXMVku8ckSqkC