Add internal links between disorder pages

[caufieldjh]

Disorder pages currently provide linkouts to MONDO PURLs but do not provide functionality to navigate to another disorder page on Dismech.
If the page on Acne Vulgaris lists Rosacea in its differential diagnosis section, for example, I would expect to be able to navigate to the Dismech page on Rosacea from that entry.

[github-actions]

Summary

This issue requests adding internal navigation links between disorder pages in the dismech knowledge base. Currently, when a disorder page (e.g., Acne Vulgaris) lists another disorder in its differential diagnosis section (e.g., Rosacea), the disorder name only links to the external MONDO ontology page, not to the corresponding dismech disorder page.

Current Implementation

The differential diagnosis section in disorder.html.j2 (lines 2321-2367) currently renders differential diagnoses with:

• Disorder name (plain text)
• MONDO term link (external to MONDO ontology)
• No internal link to the dismech disorder page

Example from disorder.html.j2 (lines 2333-2341):

<div class="item-name">
    {{ diff.name }}
    {% if diff.disease_term and diff.disease_term.term %}
    <span class="phenotype-id">
        <a href="{{ diff.disease_term.term.id | curie_to_url }}" target="_blank">
            {{ diff.disease_term.term.id }}
        </a>
    </span>
    {% endif %}
</div>

Existing Patterns for Internal Links

The codebase already has internal linking patterns in other contexts:

1. Comorbidity pages (comorbidity.html.j2:360, 376, 390, 406) link to disorder pages:

<a href="../disorders/{{ disease_a_slug }}.html">{{ disease_a_label }}</a>

2. Classification pages (classification.html.j2:133) link to disorder pages:

<a href="../disorders/{{ d.slug }}.html">{{ d.name }}</a>

3. The slugify() function (render.py:115-117) converts disorder names to URL-safe slugs:

def slugify(name: str) -> str:
    """Convert a disorder name to a filename-safe slug."""
    return name.replace(' ', '_').replace('/', '_').replace('(', '').replace(')', '')

Implementation Approach

To add internal links to differential diagnoses, the template should:

1. Convert disorder name to slug: Use the slugify() function (already available as a Jinja2 filter or callable in the template context)
2. Generate relative URL: Create a link to {{ slugify(diff.name) }}.html
3. Handle missing pages gracefully: Either check if the target page exists or accept that broken links will 404
4. Maintain MONDO link: Keep the external MONDO ontology link as supplementary information

Recommended Template Change

Replace the plain text disorder name in the differential diagnosis section with:

<div class="item-name">
    <a href="{{ diff.name | slugify }}.html">{{ diff.name }}</a>
    {% if diff.disease_term and diff.disease_term.term %}
    <span class="phenotype-id">
        <a href="{{ diff.disease_term.term.id | curie_to_url }}" target="_blank">
            {{ diff.disease_term.term.id }}
        </a>
    </span>
    {% endif %}
</div>

Or, if the slugify filter needs to be registered first in render.py:239:

env.filters['slugify'] = slugify

Data Quality Considerations

The differential diagnosis entries use the name field (free text) rather than a structured slug field, so:

• The name must match exactly with the target disorder's name for the link to resolve correctly
• Typos or variations in naming will result in 404s
• Consider validating that differential diagnosis names match existing disorder names during QC

Example from Real Data

From kb/disorders/Acne_Vulgaris.yaml:

• Differential diagnosis includes "Rosacea" (line 1037)
• Expected link target: pages/disorders/Rosacea.html
• This would allow users to navigate from Acne Vulgaris → Rosacea without leaving the dismech site

Related Sections

The same enhancement could benefit other sections that reference disorders:

• has_subtypes (line ~1524 in template)
• Parent disorders (if rendered)
• Any other cross-references between disorders

Related Issue

See #295 for a related rendering issue with empty/incomplete disorder entries that could result in broken links.