add lambda logo, fold sections, add python/error/log snippets

- Pull the rethink lambda logo (assets/img/logo.svg) into docs/assets and
  wire it as theme.logo + favicon — matches the Gitea brand mark.
- standards.md: fold six thin sections into three fuller ones (Files and
  style / Documentation / Quality and error handling), each illustrated
  with python snippets, a flake8 output block, Do/Don't tabbed examples,
  a traceback, and a log line. Admonitions for the run-it-locally tip and
  the lib-logging note.
- libraries.md: add a collapsible 'using a library' example (pyproject
  pin + import/usage python snippet).

Verified in-browser: logo renders in the header, snippets/tabs/traceback/
log blocks render against the dark theme, libraries example expands.
mkdocs build --strict clean.

Signed-off-by: disqualifier <dev@disqualifier.me>

mkdocs.yml

@@ -9,6 +9,8 @@ extra_css:
 theme:
   name: material
   language: en
+  logo: assets/logo.svg
+  favicon: assets/logo.svg
   palette:
     scheme: slate
     primary: custom