feat: support svg package — install Inkscape and enable shell-escape

The LaTeX svg package converts .svg files to PDF at compile time by
shelling out to Inkscape (requires --shell-escape). Without Inkscape in
the image and the flag enabled, compilation fails with "Did you run the
export with Inkscape?".

- Dockerfile-base: add inkscape to the apt install block
- settings.js: expose OVERLEAF_LATEX_SHELL_ESCAPE env var → clsi.latexShellEscape
- LatexRunner.js: pass -shell-escape to latexmk when the setting is on
- deploy-verso-prod.yml: set OVERLEAF_LATEX_SHELL_ESCAPE=true (trusted-user instance)

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

.gitea/workflows/deploy-verso-prod.yml

@@ -329,6 +329,8 @@ jobs:
                       # (CE default): admin creates accounts / sends invites.
                       - name: OVERLEAF_ENABLE_PROJECT_PYTHON_VENV
                         value: "true"
+                      - name: OVERLEAF_LATEX_SHELL_ESCAPE
+                        value: "true"
                       # (SMTP email vars are loaded below via envFrom.)
                     # SMTP for password-reset / invite emails. All
                     # OVERLEAF_EMAIL_* vars come from the optional 'verso-smtp'