Add Preset Library feature

Presets are saved generation recipes that combine all resource types
(character, outfit, action, style, scene, detailer, look, checkpoint)
with per-field on/off/random toggles. At generation time, entities
marked "random" are picked from the DB and fields marked "random" are
randomly included or excluded.

- Preset model + sync_presets() following existing category pattern
- _resolve_preset_entity() / _resolve_preset_fields() helpers
- Full route set: index, detail, generate, edit, upload, clone, save_json, create (LLM), rescan
- 4 templates: index (gallery), detail (summary + generate), edit (3-way toggle UI), create (LLM form)
- example_01.json reference preset + preset_system.txt LLM prompt
- Presets nav link in layout.html

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/presets/create.html

@@ -0,0 +1,80 @@
+{% extends "layout.html" %}
+
+{% block content %}
+<div class="d-flex justify-content-between align-items-center mb-4">
+    <h1>Create Preset</h1>
+    <a href="{{ url_for('presets_index') }}" class="btn btn-outline-secondary">Cancel</a>
+</div>
+
+{% with messages = get_flashed_messages(with_categories=true) %}
+{% if messages %}
+    {% for category, message in messages %}
+    <div class="alert alert-{{ 'danger' if category == 'error' else 'success' }} alert-dismissible fade show">{{ message }}<button type="button" class="btn-close" data-bs-dismiss="alert"></button></div>
+    {% endfor %}
+{% endif %}
+{% endwith %}
+
+<div class="row justify-content-center">
+    <div class="col-md-7">
+        <div class="card">
+            <div class="card-header bg-dark text-white">New Preset</div>
+            <div class="card-body">
+                <form action="{{ url_for('create_preset') }}" method="post">
+                    <div class="mb-3">
+                        <label for="name" class="form-label">Preset Name <span class="text-danger">*</span></label>
+                        <input type="text" class="form-control" id="name" name="name" required placeholder="e.g. Beach Day Casual">
+                    </div>
+
+                    <div class="mb-3">
+                        <div class="form-check form-switch">
+                            <input class="form-check-input" type="checkbox" id="use_llm" name="use_llm" checked>
+                            <label class="form-check-label" for="use_llm">Use AI to build preset from description</label>
+                        </div>
+                    </div>
+
+                    <div class="mb-3" id="description-section">
+                        <label for="description" class="form-label">Description</label>
+                        <textarea class="form-control" id="description" name="description" rows="5"
+                                  placeholder="Describe the kind of generations you want this preset to produce. Include the type of character, setting, mood, outfit style, etc.
+
+Example: A random character in a cheerful beach scene, wearing a swimsuit, with a random action pose. Always include identity and wardrobe fields. Randomise headwear and accessories. No style LoRA needed."></textarea>
+                        <div class="form-text">The AI will set entity IDs (specific, random, or none) and field toggles (on/off/random) based on your description.</div>
+                    </div>
+
+                    <div class="d-grid">
+                        <button type="submit" class="btn btn-success" id="create-btn">Create Preset</button>
+                    </div>
+                </form>
+            </div>
+        </div>
+
+        <div class="card mt-3">
+            <div class="card-header">About Presets</div>
+            <div class="card-body text-muted small">
+                <p>A <strong>preset</strong> is a saved generation recipe. It stores:</p>
+                <ul>
+                    <li><strong>Entity selections</strong> — which character, action, scene, etc. to use. Set to a specific ID, <span class="badge bg-warning text-dark">Random</span> (pick at generation time), or None.</li>
+                    <li><strong>Field toggles</strong> — which prompt fields to include. Each can be <span class="badge bg-success">ON</span>, <span class="badge bg-secondary">OFF</span>, or <span class="badge bg-warning text-dark">RNG</span> (randomly decide each generation).</li>
+                </ul>
+                <p class="mb-0">After creation you'll be taken to the edit page to review and adjust the AI's choices before generating.</p>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}
+
+{% block scripts %}
+<script>
+document.getElementById('use_llm').addEventListener('change', function() {
+    document.getElementById('description-section').style.display = this.checked ? '' : 'none';
+});
+
+document.querySelector('form').addEventListener('submit', function() {
+    const btn = document.getElementById('create-btn');
+    if (document.getElementById('use_llm').checked) {
+        btn.disabled = true;
+        btn.textContent = 'Generating with AI...';
+    }
+});
+</script>
+{% endblock %}