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/2026-05-19-api-documentation/.openspec/.pi-map.md

@@ -1,14 +1,14 @@
-# openspec/changes/archive/2026-05-19-api-documentation/.openspec
-dir: openspec/changes/archive/2026-05-19-api-documentation/.openspec
+# archive/2026-05-19-api-documentation/.openspec
+dir: archive/2026-05-19-api-documentation/.openspec
 
-index: openspec/changes/archive/2026-05-19-api-documentation/.openspec/.pi-map.index.md
+index: archive/2026-05-19-api-documentation/.openspec/.pi-map.index.md
 
 ## role
-Defines a schema-driven API documentation specification configuration for the OpenSpec changes archive.
+Defines a schema-driven API documentation specification configuration for the OpenSpec standard
 ## files
 - config.yaml | Defines a configuration file specifying a schema-driven API documentation specification
 ## arch
-YAML-based declarative configuration pattern specifying schema metadata for API documentation generation.
+YAML-based declarative configuration pattern for specifying API documentation metadata and schema references
 ## tags
 config, defines, configuration, specifying, schema, driven, api, documentation
 ## symbols