Make Start Date and Control Flag inputs optional in Periodic Notification

- Start Date: when empty, day interval is ignored and notifications fire daily
- Control Flag: when empty, notifications always fire (no toggle control)
- Update documentation to reflect optional inputs
- Fix markdown linting issues

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Common/Periodic Notification/blueprint.yaml

@@ -83,10 +83,12 @@ blueprint:
       collapsed: false
       input:
         control_flag:
-          name: Control Flag
+          name: Control Flag (optional)
           description: >
             Toggle entity to enable or disable notifications.
             Notifications are only sent when this entity is ON.
+            Leave empty to always send notifications.
+          default: ""
           selector:
             entity:
               domain:
@@ -120,6 +122,7 @@ variables:
   message_text: !input message
   interval: !input day_interval
   start_date: !input start_date
+  control_flag: !input control_flag
 
   # Debug flag - set to true to enable persistent notifications for troubleshooting
   is_debug: false
@@ -128,10 +131,14 @@ variables:
 # Conditions
 # =============================================================================
 condition:
-  # Control flag must be ON
-  - condition: state
-    entity_id: !input control_flag
-    state: "on"
+  # Control flag must be ON (skipped if no control flag)
+  - condition: template
+    value_template: >
+      {%- if control_flag | length == 0 -%}
+        true
+      {%- else -%}
+        {{ is_state(control_flag, 'on') }}
+      {%- endif -%}
 
   # Today must fall on the correct day in the interval cycle (skipped if no start date)
   - condition: template