add admin commands for system, users, gc, audit, security

Phase 6 implementation:
- system: version, auth mode, storage volumes
- gc, gc-run: schedule, history, manual trigger
- users, user-create, user-delete, user-admin, user-passwd
- audit, audit-purge: view and purge audit logs
- cve-allow: manage system CVE allowlist
- scan-all: trigger system-wide vulnerability scan

Helpers: paginated_request(), confirm_action(), format_size()

TASKLIST.md

@@ -25,8 +25,11 @@ Active, prioritized work items.
 | `labels` command | 4 |
 | `copy` command | 4 |
 | `quota` command | 4 |
+| `replication` command | 4 |
 | pyproject.toml with entry points | 5 |
 | Shell completions | 5 |
+| `registries` command | deferred |
+| `groups` command (LDAP/OIDC) | deferred |
 
 ## Completed
 
@@ -41,3 +44,9 @@ Active, prioritized work items.
 - [x] `--verify-ssl` flag for SSL certificate verification
 - [x] Modular package structure (`src/harbor/`)
 - [x] Documentation updated for new structure
+- [x] Phase 6: Admin commands (v0.1.3)
+  - `system`, `gc`, `gc-run`, `users`
+  - `user-create`, `user-delete`, `user-admin`, `user-passwd`
+  - `audit`, `audit-purge`, `cve-allow`, `scan-all`
+  - `paginated_request()` helper
+  - `confirm_action()`, `format_size()`, `format_timestamp()` helpers