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

nginx/nginx.conf.template

@@ -7,6 +7,11 @@ map $http_upgrade $connection_upgrade {
     ''      close;
 }
 
+map $uri $upload_disposition {
+    default                                                        "attachment";
+    "~*\.(jpe?g|png|gif|webp|bmp|tiff|mp4|webm|ogv|mov|m4v|mp3)$"  "inline";
+}
+
 proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=app_cache:10m max_size=${NGINX_CACHE_MAX_SIZE} inactive=60m use_temp_path=off;
 
 server {
@@ -29,7 +34,7 @@ server {
     location /static/uploads/ {
         alias /app/static/uploads/;
         add_header X-Content-Type-Options nosniff;
-        add_header Content-Disposition attachment;
+        add_header Content-Disposition $upload_disposition;
         add_header Cache-Control "public, max-age=604800";
         access_log off;
         log_not_found off;