Markdown support for description fields added; Tests updated

AGENTS.md

@@ -218,7 +218,7 @@ labhelper/
 │   │       ├── search.html                 # Search page with AJAX
 │   │       └── thing_detail.html           # Thing details view with tags
 │   ├── templatetags/
-│   │   └── dict_extras.py                  # Custom template filter: get_item
+│   │   └── dict_extras.py                  # Custom template filters: get_item, render_markdown, truncate_markdown
 │   ├── admin.py                            # Admin configuration
 │   ├── apps.py                             # App configuration
 │   ├── forms.py                            # All forms and formsets
@@ -260,7 +260,7 @@ labhelper/
 | **Box** | A storage box in the lab | `id` (CharField PK, max 10), `box_type` (FK) |
 | **Facet** | A category of tags (e.g., Priority, Category) | `name`, `slug`, `color`, `cardinality` (single/multiple) |
 | **Tag** | A tag value for a specific facet | `facet` (FK), `name` |
-| **Thing** | An item stored in a box | `name`, `box` (FK), `description`, `picture`, `tags` (M2M) |
+| **Thing** | An item stored in a box | `name`, `box` (FK), `description` (Markdown), `picture`, `tags` (M2M) |
 | **ThingFile** | File attachment for a Thing | `thing` (FK), `file`, `title`, `uploaded_at` |
 | **ThingLink** | Hyperlink for a Thing | `thing` (FK), `url`, `title`, `uploaded_at` |
 
@@ -397,41 +397,86 @@ The project uses a base template system at `labhelper/templates/base.html`. All
 ### Template Best Practices
 
 1. **Always extend base template**
-   ```django
-   {% extends "base.html" %}
-   ```
+    ```django
+    {% extends "base.html" %}
+    ```
 
 2. **Use block system for content injection**
-   - `title`: Page title tag
-   - `page_header`: Page header with breadcrumbs
-   - `content`: Main page content
-   - `extra_css`: Additional styles
-   - `extra_js`: Additional JavaScript
+    - `title`: Page title tag
+    - `page_header`: Page header with breadcrumbs
+    - `content`: Main page content
+    - `extra_css`: Additional styles
+    - `extra_js`: Additional JavaScript
 
 3. **Load required template tags**
-   ```django
-   {% load static %}
-   {% load mptt_tags %}
-   {% load thumbnail %}
-   ```
+    ```django
+    {% load static %}
+    {% load mptt_tags %}
+    {% load thumbnail %}
+    {% load dict_extras %}
+    ```
 
 4. **Use URL names for links**
-   ```django
-   <a href="{% url 'box_detail' box.id %}">
-   ```
+    ```django
+    <a href="{% url 'box_detail' box.id %}">
+    ```
 
 5. **Use icons with Font Awesome**
-   ```django
-   <i class="fas fa-box"></i>
-   ```
+    ```django
+    <i class="fas fa-box"></i>
+    ```
 
 6. **Add breadcrumbs for navigation**
-   ```django
-   <p class="breadcrumb">
-       <a href="/"><i class="fas fa-home"></i> Home</a> / 
-       <a href="/box/{{ box.id }}/"><i class="fas fa-box"></i> Box {{ box.id }}</a>
-   </p>
-   ```
+    ```django
+    <p class="breadcrumb">
+        <a href="/"><i class="fas fa-home"></i> Home</a> / 
+        <a href="/box/{{ box.id }}/"><i class="fas fa-box"></i> Box {{ box.id }}</a>
+    </p>
+    ```
+
+### Markdown Support
+
+The `Thing.description` field supports Markdown formatting with HTML sanitization for security.
+
+**Available Template Filters:**
+
+- `render_markdown`: Converts Markdown text to sanitized HTML with automatic link handling
+  - Converts Markdown syntax (headers, lists, bold, italic, links, code, tables, etc.)
+  - Sanitizes HTML using `bleach` to prevent XSS attacks
+  - Automatically adds `target="_blank"` and `rel="noopener noreferrer"` to external links
+  - Use in `thing_detail.html` for full rendered Markdown
+
+- `truncate_markdown`: Converts Markdown to plain text and truncates
+  - Strips HTML tags after Markdown conversion
+  - Adds ellipsis (`...`) if text exceeds specified length (default: 100)
+  - Use in `box_detail.html` or search API previews where space is limited
+
+**Usage Examples:**
+```django
+<!-- Full Markdown rendering -->
+<div class="markdown-content">
+    {{ thing.description|render_markdown }}
+</div>
+
+<!-- Truncated plain text preview -->
+{{ thing.description|truncate_markdown:100 }}
+```
+
+**Supported Markdown Features:**
+- Bold: `**text**` or `__text__`
+- Italic: `*text*` or `_text_`
+- Headers: `# Header 1`, `## Header 2`, etc.
+- Lists: `- item` or `1. item`
+- Links: `[text](url)`
+- Code: `` `code` `` or ` ```code block``` 
+- Blockquotes: `> quote`
+- Tables: `| A | B |\n|---|---|`
+
+**Security:**
+- All Markdown is sanitized before rendering
+- Dangerous HTML tags (`<script>`, `<iframe>`, etc.) are stripped
+- Only safe HTML tags and attributes are allowed
+- External links automatically get `target="_blank"` and security attributes
 
 ## Forms