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-tool-instances/.openspec/.pi-map.md

@@ -1,14 +1,14 @@
-# openspec/changes/archive/2026-05-19-tool-instances/.openspec
-dir: openspec/changes/archive/2026-05-19-tool-instances/.openspec
+# archive/2026-05-19-tool-instances/.openspec
+dir: archive/2026-05-19-tool-instances/.openspec
 
-index: openspec/changes/archive/2026-05-19-tool-instances/.openspec/.pi-map.index.md
+index: archive/2026-05-19-tool-instances/.openspec/.pi-map.index.md
 
 ## role
-Defines the OpenSpec schema configuration for a specific archived version of tool instances from May 19, 2026.
+Defines the OpenAPI specification schema configuration for tool instance metadata.
 ## files
 - config.yaml | Defines a configuration file specifying a schema type and name for tool instances.
 ## arch
-Simple declarative schema metadata pattern using YAML configuration files to specify schema type and name identifiers.
+Simple declarative configuration using YAML to specify schema types and naming conventions.
 ## tags
 config, defines, configuration, specifying, schema, type, name, tool
 ## symbols