chore: restructure firmware into subdirectory, add DDEV config

Move firmware files from repo root src/ into firmware/ to avoid
collision with Symfony's src/ PHP class directory. Add DDEV
config targeting PHP 8.4 / PostgreSQL 16 / nginx-fpm with
Imagick extension via docker-compose override.

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

.ddev/docker-compose.imagick.yaml

@@ -0,0 +1,12 @@
+services:
+  web:
+    build:
+      context: .
+      dockerfile_inline: |
+        ARG BASE_IMAGE
+        FROM $BASE_IMAGE
+        RUN apt-get update && apt-get install -y \
+          libmagickwand-dev \
+          && pecl install imagick \
+          && docker-php-ext-enable imagick \
+          && rm -rf /var/lib/apt/lists/*