docs: add maintenance guide; fix AppImage version selection; bump to 1.1.0

- Add MAINTENANCE.md (dependency updates, EOL watch, build/smoke-test
  workflows, orientation-fix invariants)
- Remove AGENTS.md; fold its unique context into MAINTENANCE.md
- Add .venv/.posit/appimage to .dockerignore to shrink build context
- Fix build-appimage.sh to select the wheel matching pyproject.toml
  version instead of alphabetically-first (bundled stale 1.0.0 code)
- Bump version 1.0.0 -> 1.1.0 in pyproject.toml, uv.lock, AppImage recipe

uv.lock

@@ -222,7 +222,7 @@ wheels = [
 
 [[package]]
 name = "scanslicer"
-version = "1.0.0"
+version = "1.1.0"
 source = { editable = "." }
 dependencies = [
     { name = "numpy", version = "2.2.6", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.11'" },