fix: complete the docs/→design/ and openapi→api/ rename references

The file moves (docs/ → design/, docs/api/openapi.json → api/openapi.json) landed
in d01a8fd, but the matching reference updates did not — so mgmt.rs's drift-test
`include_str!("../../../docs/api/openapi.json")` pointed at a path that no longer
exists and the host failed to build. This restores it and updates every reference:

  - mgmt.rs include_str! → ../../../api/openapi.json (fixes the build)
  - web/orval.config.ts codegen target, web/Dockerfile, .dockerignore
  - deb/rpm/Arch packaging install paths
  - CLAUDE.md, the .gitea CI workflows, code doc-comments, design-doc cross-links

docs-site route URLs (/docs/...) untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/headless/run-headless-sway.sh

@@ -5,7 +5,7 @@
 # ScreenCast portal (xdg-desktop-portal-wlr) and the punktfunk host share one bus. After this
 # is up, run `prepare-session.sh` from a second shell to set the mode + portal env.
 #
-# Prereqs (see docs/linux-setup.md / scripts/bootstrap-ubuntu.sh):
+# Prereqs (see design/linux-setup.md / scripts/bootstrap-ubuntu.sh):
 #   - nvidia-drm.modeset=Y
 #   - the NVIDIA GL/EGL userspace (libnvidia-gl-NNN) — provides libEGL_nvidia + the GLVND
 #     vendor JSON; without it wlroots can't init EGL on the GPU and falls back to pixman,