feat: add project file system with CRUD, upload, inline editing, and video attachment support

- Add new `/projects/{slug}/files` endpoint group for per-project filesystem operations including directory and file CRUD, upload, and inline editing with public read and owner write access
- Extend attachment system to support video formats (webm, ogv, mov, m4v) with proper file icons and MIME types
- Implement configurable allowed file types via `allowed_file_types` site setting, replacing hardcoded `ALLOWED_UPLOAD_TYPES` with dynamic `allowed_extensions()` and `is_extension_allowed()` functions
- Add `delete_all_project_files()` call in `delete_content_item()` to clean up project files when a project is deleted
- Create database indexes on `project_files` table for `(project_uid, path)` and `(project_uid, parent_path)` to optimize file lookups
- Introduce `docs_prose.py` module with `render_prose()` function that renders Markdown content inside `data-render` divs using mistune, enabling dynamic prose rendering in documentation pages
- Enhance docs search with Markdown-aware text stripping (`_demarkdown()`) and improved HTML/script/style sanitization for better search indexing
- Update documentation API samples to reflect new attachment response fields (`is_image`, `is_video`, `mime_type`) and note video format support
- Update README to document the new project files endpoint and clarify AI gateway attribution for guest Devii sessions

devplacepy/templates/project_detail.html

@@ -53,6 +53,7 @@
         {% endif %}
 
         <div class="project-detail-actions">
+            <a href="/projects/{{ project['slug'] or project['uid'] }}/files" class="project-star-btn">&#x1F4C1; Files</a>
             <button type="button" class="project-star-btn" data-share="/projects/{{ project['slug'] or project['uid'] }}">&#x1F517; Share</button>
             {% if user %}
             {% set _type = "project" %}{% set _uid = project['uid'] %}{% set _my_vote = my_vote %}{% set _count = star_count %}{% set _btn_class = "project-star-btn" %}{% include "_star_vote.html" %}