Reorganize into src/ with script/assets/templates, illustration/ at root

New layout:
  src/script/app/    Python package (was app/)
  src/assets/img/    SVGs (was static/*.svg)
  src/assets/css/    stylesheet (was static/style.css)
  src/templates/     HTML templates (was templates/)
  illustration/      README screenshot (was screenshots/), kept at
                      the repo root since it's a doc asset, not
                      something the app serves
  main.py, jobs/, VERSION, docker/  unchanged locations

main.py stays at the repo root as the entry point (matches how
Docker and local runs already invoke it) and prepends src/script to
sys.path before importing app, rather than moving into src/script/
itself and needing every entry point updated to match.

config.py's path constants are recomputed for app/config.py's new
depth (src/script/app/), with SRC_DIR and REPO_ROOT resolved
explicitly rather than a single ambiguous BASE_DIR, since "templates
and assets live under src/" and "jobs and VERSION live at the repo
root" are no longer the same directory. Flask's static_folder now
points at src/assets, which serves img/ and css/ under it at
whatever URL prefix Flask derives from the folder name (/assets, not
/static); templates already reference assets via the "static"
endpoint name through url_for, so this needed the url_for() calls'
filename argument updated with the img/ or css/ prefix, not a
hardcoded URL change.

Docker copies src/ into the image preserving this same internal
structure, so the path arithmetic in config.py resolves identically
in both a local checkout and the container, no --chdir or other
container-specific path handling needed.

Verified end to end after the move: local Flask dev server, a full
Docker rebuild, and a real HTTP conversion request through the
running container (TIFF HDR pipeline, numpy/tifffile imports
included) all succeed.

docker/Dockerfile

@@ -27,9 +27,7 @@ COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 COPY main.py .
-COPY app/ app/
-COPY templates/ templates/
-COPY static/ static/
+COPY src/ src/
 COPY LICENSE VERSION ./
 COPY docker/entrypoint.sh /app/entrypoint.sh
 RUN chmod +x /app/entrypoint.sh