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/2026-06-12-completed-changes-archive/README.md

@@ -0,0 +1,30 @@
+# Archived Completed Changes — 2026-06-12
+
+These OpenSpec changes have been audited against the current source tree and confirmed as fully implemented. They are archived here for historical reference.
+
+## Archived changes
+
+- 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
+
+## Audit summary
+
+| Status | Count |
+|--------|-------|
+| Fully implemented | 15 |
+| Partially implemented | 0 (in this archive) |
+
+Audit report: `/tmp/active-changes-implementation-audit.md` (generated before archiving).