chore(docs): bump dependencies and adapt to fumadocs-core 16.15.11

Updates the docs site's dependencies, including the Fumadocs packages,
Next 16.3.5, React 19.3 and three majors: mermaid 12, vitest 5 and
pnpm 12. Two code changes follow from the bump:

- fumadocs-core 16.15.11 makes `llms().index()` return a Promise, so
  the llms.txt route now awaits it; tsc rejected the old synchronous
  call
- lucide-react 1.46 renamed the BookMarked icon to BookBookmark. The
  old name is still exported, but lucideIconsPlugin looks names up in
  lucide's `icons` map, which only has the new one, so the Reference
  section lost its sidebar icon in all four locales. The build only
  printed a warning.

minimumReleaseAgeExclude gains entries for the newly installed
versions.

Checked with typecheck, lint, vitest (106 tests) and a full build: no
plugin warnings, and each locale's rendered /docs page contains the
book-bookmark icon.

docs/pnpm-workspace.yaml

@@ -12,9 +12,16 @@ minimumReleaseAgeExclude:
   - mermaid@11.17.0
   - lucide-react@1.33.0
   - postcss@8.5.26
-  - fumadocs-mdx@15.3.0
-  - '@fumadocs/api-docs@0.2.7'
+  - fumadocs-mdx@15.3.0 || 15.4.1
+  - '@fumadocs/api-docs@0.2.7 || 0.2.9'
   - '@types/node@26.4.1'
-  - fumadocs-core@16.15.5
-  - fumadocs-openapi@11.4.0
-  - fumadocs-ui@16.15.5
+  - fumadocs-core@16.15.5 || 16.15.11
+  - fumadocs-openapi@11.4.0 || 11.4.3
+  - fumadocs-ui@16.15.5 || 16.15.11
+  - '@fumadocs/tailwind@0.1.2'
+  - '@fumari/image-size@0.1.1'
+  - '@fumari/stf@1.1.1'
+  - '@vitest/mocker@5.0.1'
+  - '@vitest/spy@5.0.1'
+  - fumadocs-docgen@3.1.1
+  - vitest@5.0.1