Auto-register borg repo on the controller per host

backup role now logs into borgcontroller and creates (or looks up) a
repository with alias=inventory_hostname, registering root's pubkey and
the requested storageSize. The resulting SSH URI is injected into the
borgmatic config so each host gets a remote-managed repo without manual
config.

backup_hosts entries gain a `storage_size_gb` field (stripped before
templating) and lose the manual `repositories` entry — the role fills it.
borgcontroller_{username,password} are expected from Semaphore secrets.

Also gitignores .claude/ local state.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -5,3 +5,6 @@ venv/
 # MikroTik backup output
 mikrotik/backups/
 mikrotik/output/
+
+# Claude Code local state
+.claude/