MkDocs documentation is skeletal — add API reference and comprehensive usage guides

[soumendrak]

Current state: The MkDocs site at https://openodia.soumendrak.com has only 3 pages (index.md, application.md, and a cover image). While the index page is thorough with inline examples, there is:

• No auto-generated API reference from docstrings
• No dedicated module-by-module documentation pages
• No "Getting Started" quickstart guide separate from the full README
• No changelog/release notes page
• No searchable API index

Suggested improvements:

1. Generate API reference from docstrings using mkdocstrings (Python handler). Every public function/class in the 14 modules (alphabet, numbers, syllable, segment, stats, stopwords, text, cache, corpus, etc.) should have a rendered reference page.

2. Add dedicated pages per module with:

   • Usage examples beyond what's in the monolithic index
   • Edge cases and gotchas
   • Performance notes (e.g., translation LRU cache sizing)

3. Add a changelog page that tracks releases (can be auto-generated from git tags with mkdocs-git-revision-date-localized-plugin which is already a dependency).

4. Add a "Contributing" guide page that goes beyond the one-liner in CONTRIBUTING.md.

5. Enable search — mkdocs-material has built-in search via lunr.js; it should be fully wired. Currently include_search_page: false and search_index_only: true in mkdocs.yml limits functionality.

Why this matters: Quality documentation lowers the contribution barrier, helps users discover all 14+ modules, and is essential for a package aiming to be the standard Odia NLP library. The codebase has excellent docstrings already — they just need to be surfaced.

Suggested approach:

• Add mkdocstrings and mkdocs-gen-files to the docs extra
• Create a docs/api/ folder with one .md stub per module that uses ::: openodia.module syntax
• Structure navigation in mkdocs.yml with sections: Getting Started → API Reference → Applications → Contributing → Changelog