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>

crates/punktfunk-host/src/windows/wgc_helper.rs

@@ -1,5 +1,5 @@
 //! USER-session WGC helper (Windows) — part of the two-process secure-desktop design
-//! (docs/windows-secure-desktop.md).
+//! (design/windows-secure-desktop.md).
 //!
 //! WGC won't activate under the SYSTEM account, but the host must run as SYSTEM for the secure
 //! desktop. So the SYSTEM host spawns THIS helper in the interactive user session