Use a typed escalation fallback instead of fallbackTopic

TerdutTeam spec.escalation.fallback is now {type, address}, mirroring the
server's notification channel model. CRDs regenerated.

Claude-Session: https://claude.ai/code/session_016mBLURvJoMuUEr9cB2RpUN

config/crd/bases/terdut.ryuvia.com_terdutteams.yaml

@@ -113,8 +113,28 @@ spec:
                   escalation is this team's escalation ladder. Omitted, the team has none
                   (the server's plain reminder behaviour applies).
                 properties:
-                  fallbackTopic:
-                    type: string
+                  fallback:
+                    description: |-
+                      fallback is paged once when the ladder has run out of levels and repeats.
+                      Omitted, the chain just ends there.
+                    properties:
+                      address:
+                        description: 'address is where that provider delivers it:
+                          an ntfy topic, say.'
+                        maxLength: 256
+                        minLength: 1
+                        type: string
+                      type:
+                        description: |-
+                          type is the notification provider, e.g. "ntfy". The server refuses a
+                          provider it has not been configured with.
+                        maxLength: 32
+                        minLength: 1
+                        type: string
+                    required:
+                    - address
+                    - type
+                    type: object
                   levels:
                     items:
                       description: |-