Migrate from mkdocs to properdocs

- Replace mkdocs-with-pdf + weasyprint with properdocs>=1.6.7
- Add pymdown-extensions for richer markdown support
- Remove heavy apt dependencies (weasyprint, fonts-noto-cjk, wget, unzip)
- Switch build command from 'mkdocs build' to 'properdocs build --strict'
- Update template: add offline plugin, fix palette, add content.code.select/copy
- Add md_in_html, pymdownx.tilde, emoji, mermaid, annotation icon support
- Fix broken icon path material//weather-sunny

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Dockerfile

@@ -12,9 +12,8 @@ RUN npm run lint
 FROM python:3.11 AS python-env
 WORKDIR /app
 COPY --from=lint-env /app .
-RUN apt-get update && apt-get install -y weasyprint fonts-noto-cjk wget unzip
 RUN rm node_modules -rf && pip install -r requirements.txt
-RUN mkdocs build
+RUN python3 -m properdocs build --strict
 
 # ============================
 # Prepare Runtime Environment