Add comprehensive documentation for URL namespacing

[rtibbles]

Summary

• New how-to guide: "Working with URLs and API Endpoints" that covers:

  • URL naming conventions (kolibri:namespace:resource_endpoint)
  • How to define URLs in Django backend (ViewSets, routers, custom URLs)
  • How to use URLs in JavaScript frontend (direct access, API Resources)
  • Complete explanation of the backend-to-frontend URL pipeline
  • Best practices and debugging tips
  • Advanced topics (custom endpoints, direct endpoint access)

• Updated existing API endpoints documentation with URL namespacing overview and cross-reference to the new guide

• Updated frontend core architecture documentation to explain URL namespacing with practical examples

• Added the new guide to the howtos index

The documentation explains how URL namespacing works implicitly in the API resource layer and explicitly in frontend code (e.g., urls['kolibri:core:driveinfo-list']), providing developers with a complete understanding of the system.

References

Fixes #9435

Reviewer guidance

:exclamation: 🤖 Generated with Claude Code :exclamation:

Are there any parts that are too verbose, and just add fluff rather than useful variation? Are there any explicitly duplicative parts? Any inaccuracies?

[github-actions[bot]]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.19.0b1.dev0_git.60.g3eae1bdc.pex
Windows Installer (EXE)	kolibri-0.19.0b1.dev0+git.60.g3eae1bdc-windows-setup-unsigned.exe
Debian Package	kolibri_0.19.0b1.dev0+git.60.g3eae1bdc-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.19.0b1.dev0+git.60.g3eae1bdc.dmg
Android Package (APK)	kolibri-0.19.0b1.dev0+git.60.g3eae1bdc-0.1.6-debug.apk
Raspberry Pi Image	kolibri-pi-image-0.19.0b1.dev0+git.60.g3eae1bdc.zip
TAR file	kolibri-0.19.0b1.dev0+git.60.g3eae1bdc.tar.gz
WHL file	kolibri-0.19.0b1.dev0+git.60.g3eae1bdc-py2.py3-none-any.whl

[rtibbles]

This is potentially still a little verbose for my taste - but I'd rather have input from others about whether these are useful additional examples and documentation or just unnecessary verbiage.