Simplify docs config with theme mixins (#56)

## Summary
- Delete `docs/hooks.py` — all preprocessing logic (matplotlib rcParams,
MyST admonition conversion, cross-ref auto-linking) is now handled by
shadcn theme mixins
- Remove all `markdown_extensions` and `mkdocstrings` options
boilerplate from `mkdocs.yml` — theme provides sensible defaults
- Add `crossref_modules` and `crossref_aliases` to theme config for
project-specific cross-ref resolution

Net result: `mkdocs.yml` goes from 90 to 56 lines, `hooks.py` (112
lines) is deleted entirely.

Depends on gdsfactory/mkdocs-shadcn@13d85fc.

## Test plan
- [ ] `just docs` builds without errors
- [ ] Syntax highlighting works on notebook pages
- [ ] Cross-refs resolve on API page
- [ ] KaTeX math renders on algorithm page

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: flaport

docs/hooks.py

@@ -11,6 +11,13 @@ theme:
   logo: assets/logo-small.svg
   favicon: assets/logo-small.ico
   katex_options: {}
+  crossref_modules:
+    - meow
+    - meow.eme
+    - meow.fde
+  crossref_aliases:
+    compute_modes: meow.compute_modes_tidy3d
+    compute_s_matrix: meow.compute_s_matrix_sax
 
 nav:
   - home: index.md
@@ -25,9 +32,6 @@ nav:
   - api: api.md
   - changelog: changelog.md
 
-hooks:
-  - docs/hooks.py
-
 plugins:
   - search
   - autorefs
@@ -49,41 +53,3 @@ plugins:
             - https://scipy.github.io/devdocs/objects.inv
             - https://typing.readthedocs.io/en/latest/objects.inv
             - https://www.mkdocs.org/objects.inv
-          options:
-            allow_inspection: true
-            docstring_style: google
-            docstring_options:
-              ignore_init_summary: true
-            docstring_section_style: table # table | list | spacy
-            filters: ["!^_"]
-            heading_level: 1
-            inherited_members: true
-            merge_init_into_class: true
-            separate_signature: true
-            show_root_heading: true
-            show_root_full_path: false
-            show_signature_annotations: true
-            show_source: true
-            show_symbol_type_heading: true
-            show_symbol_type_toc: true
-            signature_crossrefs: true
-            summary: true
-
-markdown_extensions:
-  - attr_list
-  - toc:
-      permalink: true
-  - pymdownx.highlight:
-      anchor_linenums: true
-      line_spans: __span
-      pygments_lang_class: true
-  - pymdownx.inlinehilite
-  - pymdownx.snippets
-  - pymdownx.magiclink
-  - pymdownx.tabbed:
-      alternate_style: true
-  - admonition
-  - pymdownx.details
-  - pymdownx.arithmatex:
-      generic: true
-  - pymdownx.superfences