feat: initialize Apex Theme System with build engine and Neovim template

- Set up project structure and Source of Truth (GEMINI.md).
- Implement DNA source files (src/*.yaml) with semantic color definitions.
- Build clinical light (Aeon) and high-contrast dark (Neon) specifications.
- Create Jinja2-based build system (build.py) using uv for reproducibility.
- Implement Neovim theme template mirroring the philosophy.

build.py

@@ -0,0 +1,64 @@
+import yaml
+import os
+from jinja2 import Environment, FileSystemLoader
+
+# Configuration
+SRC_DIR = 'src'
+TEMPLATES_DIR = 'templates'
+DIST_DIR = 'dist'
+SCHEMES = ['neon.yaml', 'aeon.yaml']
+
+def load_scheme(filename):
+    with open(os.path.join(SRC_DIR, filename), 'r') as f:
+        return yaml.safe_load(f)
+
+def render_template(template_path, context):
+    env = Environment(loader=FileSystemLoader(TEMPLATES_DIR))
+    template = env.get_template(template_path)
+    return template.render(context)
+
+def build():
+    # Ensure dist directory exists
+    if not os.path.exists(DIST_DIR):
+        os.makedirs(DIST_DIR)
+
+    for scheme_file in SCHEMES:
+        scheme_data = load_scheme(scheme_file)
+        scheme_name_slug = scheme_data['scheme'].lower().replace(' ', '-')
+        print(f"Building {scheme_data['scheme']}...")
+
+        # Find all templates
+        for root, dirs, files in os.walk(TEMPLATES_DIR):
+            for file in files:
+                if file.endswith('.j2'):
+                    # Calculate relative path to mirror structure in dist
+                    rel_path = os.path.relpath(root, TEMPLATES_DIR)
+                    template_rel_path = os.path.join(rel_path, file)
+                    
+                    # Prepare output path
+                    output_filename = file.replace('.j2', '')
+                    # If the template is generic (apex.lua), rename it to the scheme name (apex-neon.lua)
+                    if 'apex' in output_filename:
+                        output_filename = output_filename.replace('apex', scheme_name_slug)
+                    
+                    output_dir = os.path.join(DIST_DIR, scheme_name_slug, rel_path)
+                    if not os.path.exists(output_dir):
+                        os.makedirs(output_dir)
+                    
+                    output_path = os.path.join(output_dir, output_filename)
+                    
+                    # Render and write
+                    # We pass template_rel_path because jinja loader is rooted at TEMPLATES_DIR
+                    # But os.walk returns paths relative to CWD usually, but we constructed it.
+                    # Actually Environment loader is correct. We just need the path relative to templates dir.
+                    template_name_for_jinja = template_rel_path
+                    
+                    rendered_content = render_template(template_name_for_jinja, scheme_data)
+                    
+                    with open(output_path, 'w') as f:
+                        f.write(rendered_content)
+                    
+                    print(f"  -> {output_path}")
+
+if __name__ == '__main__':
+    build()