Remove pre-package-restructure cruft and dead features

Delete the top-level implementation superseded by the gallery/ package
conversion (generate_gallery.py, orchestration/, root templates/ and
assets/, python/ scripts), stray scratch files, and docs describing a
container/GitLab-CI coverage workflow that no longer exists. Also drop
two half-wired, never-invoked features: the backup_folder config/TUI
option (create_backup() was never called from the pipeline) and the
unfinished export-to-LaTeX JS/CSS. Update README's install instructions
to the current Gitea remote.

README.md

@@ -38,12 +38,12 @@
 
 ## Installation
 
-### From GitLab
+### From Gitea
 
 Pip install:
 
 ```bash
-pip install git+https://gitlab.etp.kit.edu/kschmidt/web
+pip install git+https://git.larsbogner.de/lars/ETPlot
 ```
 
 Or git clone and `pip install .`. After installation the `gallery` command is available in your shell. Verify with:
@@ -184,7 +184,6 @@ paths:
 gallery:
   plot_root: "gallery"       # subdirectory inside web_folder
   png_dpi: 400               # thumbnail resolution
-  backup_folder: ""          # optional backup path
 
 sources:
   - name: "analysis_results"