chore: archive 15 completed OpenSpec changes

Move the following audited-and-implemented changes into
openspec/changes/archive/2026-06-12-completed-changes-archive/:

- backend-frontend-refactoring
- config-profile-git-mounts
- config-profile-includes-ui
- config-profile-multi-repo-mounts
- container-monitoring-notifications
- git-mount-url-validation
- home-path-expansion
- mobile-terminal-ux
- mount-specificity-ordering
- notification-center
- persistent-terminal-sessions
- session-list-overhaul
- ssh-key-mounting
- terminal-fullscreen-unified-header
- tool-session-progress-and-updates

Also regenerated .pi-map*.md files for openspec/changes so the
remaining active changes (multi-session-terminal-ux, reorganize-long-files,
working-copies, workspace-first-ui) reflect the new layout.

openspec/changes/archive/2025-05-17-oauth-traefik-integration/specs/.pi-map.md

@@ -1,13 +1,13 @@
-# openspec/changes/archive/2025-05-17-oauth-traefik-integration/specs
-dir: openspec/changes/archive/2025-05-17-oauth-traefik-integration/specs
+# archive/2025-05-17-oauth-traefik-integration/specs
+dir: archive/2025-05-17-oauth-traefik-integration/specs
 
-index: openspec/changes/archive/2025-05-17-oauth-traefik-integration/specs/.pi-map.index.md
+index: archive/2025-05-17-oauth-traefik-integration/specs/.pi-map.index.md
 
 ## role
-Contains specification documents for OAuth-Traefik integration architecture implemented on 2025-05-17, serving as archived design reference for the project's authentication/authorization infrastructure.
+Contains specification documents for OAuth-Traefik integration design.
 ## files
 ## arch
-Specification-driven architecture using archived dated design documents for reverse-proxy-based OAuth integration, likely detailing Traefik middleware configuration patterns for external authentication providers.
+Documentation-only package with no code architecture; stores technical specifications and design documents.
 ## tags
 -
 ## symbols