Add back-to-planet navigation from moons to host planet

Enhanced moon navigation to allow easy return to the host planet's details.
Previously, moon navigation only had "leave_jupiter" which took you to the
final navigation menu. Now you can also go back to see the planet itself.

New Navigation Pattern (implemented for Jupiter's moons):

From any moon, you can now:
1. **Jump to other moons** - "Europa", "Ganymede", etc.
2. **Return to moon menu** - "moon menu" shows all moon options
3. **Back to planet** - "Jupiter" or "back to Jupiter" returns to planet details
4. **Leave entirely** - "leave Jupiter" goes to planet-to-planet navigation

Example Navigation Flow:
- Visit Jupiter → See planet details
- Choose "Io" → See Io's volcanoes
- Say "back to Jupiter" → Return to Jupiter's details (storms, bands, etc.)
- Say "Europa" → Jump directly to Europa
- Say "leave Jupiter" → Continue to Saturn

Updated Navigation Steps:
- moon_io_nav: Added back_to_planet → jupiter:jupiter_details
- moon_europa_nav: Added back_to_planet → jupiter:jupiter_details
- moon_ganymede_nav: Added back_to_planet → jupiter:jupiter_details
- moon_callisto_nav: Added back_to_planet → jupiter:jupiter_details
- jupiter_other_moons_nav: Added back_to_planet → jupiter:jupiter_details

This same pattern can be extended to Saturn, Uranus, and Neptune moons,
allowing seamless navigation: Moon → Moon, Moon → Planet, Planet → Planet.

research/activity38-solar-system-explorer.yaml

@@ -1048,9 +1048,10 @@ sections:
           - 'callisto' if they mention callisto
           - 'other_moons' if they mention other moons, small moons
           - 'moon_menu' if they want to choose from menu, see list, back to moons
-          - 'leave_jupiter' if they want to leave Jupiter, go elsewhere, other planets
+          - 'back_to_planet' if they want to see Jupiter again, back to jupiter, jupiter details, planet
+          - 'leave_jupiter' if they want to leave Jupiter entirely, go elsewhere, other planets
           - 'stay' if they have questions about Io
-        buckets: [europa, ganymede, callisto, other_moons, moon_menu, leave_jupiter, stay]
+        buckets: [europa, ganymede, callisto, other_moons, moon_menu, back_to_planet, leave_jupiter, stay]
         transitions:
           europa:
             ai_feedback:
@@ -1072,6 +1073,10 @@ sections:
             ai_feedback:
               tokens_for_ai: "Back to the moon selection menu!"
             next_section_and_step: "jupiter:jupiter_moon_menu"
+          back_to_planet:
+            ai_feedback:
+              tokens_for_ai: "Returning to Jupiter!"
+            next_section_and_step: "jupiter:jupiter_details"
           leave_jupiter:
             ai_feedback:
               tokens_for_ai: "Ready to continue your journey!"
@@ -1125,9 +1130,10 @@ sections:
           - 'callisto' if they mention callisto
           - 'other_moons' if they mention other moons, small moons
           - 'moon_menu' if they want moon menu, choose from list
-          - 'leave_jupiter' if they want to leave Jupiter
+          - 'back_to_planet' if they want to see Jupiter, back to jupiter, planet
+          - 'leave_jupiter' if they want to leave Jupiter entirely, other planets
           - 'stay' if they have Europa questions
-        buckets: [io, ganymede, callisto, other_moons, moon_menu, leave_jupiter, stay]
+        buckets: [io, ganymede, callisto, other_moons, moon_menu, back_to_planet, leave_jupiter, stay]
         transitions:
           io:
             ai_feedback:
@@ -1149,6 +1155,10 @@ sections:
             ai_feedback:
               tokens_for_ai: "Back to the moon menu!"
             next_section_and_step: "jupiter:jupiter_moon_menu"
+          back_to_planet:
+            ai_feedback:
+              tokens_for_ai: "Returning to Jupiter!"
+            next_section_and_step: "jupiter:jupiter_details"
           leave_jupiter:
             ai_feedback:
               tokens_for_ai: "Continuing your solar system journey!"
@@ -1202,9 +1212,10 @@ sections:
           - 'callisto' if they mention callisto, ancient, next
           - 'other_moons' if they mention other, small moons
           - 'moon_menu' if they want the menu
-          - 'leave_jupiter' if leaving Jupiter
+          - 'back_to_planet' if they want to see Jupiter, back to jupiter, planet
+          - 'leave_jupiter' if leaving Jupiter entirely, other planets
           - 'stay' for Ganymede questions
-        buckets: [io, europa, callisto, other_moons, moon_menu, leave_jupiter, stay]
+        buckets: [io, europa, callisto, other_moons, moon_menu, back_to_planet, leave_jupiter, stay]
         transitions:
           io:
             ai_feedback:
@@ -1226,6 +1237,10 @@ sections:
             ai_feedback:
               tokens_for_ai: "Back to moon selection!"
             next_section_and_step: "jupiter:jupiter_moon_menu"
+          back_to_planet:
+            ai_feedback:
+              tokens_for_ai: "Returning to Jupiter!"
+            next_section_and_step: "jupiter:jupiter_details"
           leave_jupiter:
             ai_feedback:
               tokens_for_ai: "Continuing your journey!"
@@ -1278,9 +1293,10 @@ sections:
           - 'ganymede' if they mention ganymede
           - 'other_moons' if they mention other moons, small, irregular
           - 'moon_menu' if they want menu
-          - 'leave_jupiter' if leaving
+          - 'back_to_planet' if they want to see Jupiter, back to jupiter, planet
+          - 'leave_jupiter' if leaving entirely, other planets
           - 'stay' for Callisto questions
-        buckets: [io, europa, ganymede, other_moons, moon_menu, leave_jupiter, stay]
+        buckets: [io, europa, ganymede, other_moons, moon_menu, back_to_planet, leave_jupiter, stay]
         transitions:
           io:
             ai_feedback:
@@ -1302,6 +1318,10 @@ sections:
             ai_feedback:
               tokens_for_ai: "Back to the menu!"
             next_section_and_step: "jupiter:jupiter_moon_menu"
+          back_to_planet:
+            ai_feedback:
+              tokens_for_ai: "Returning to Jupiter!"
+            next_section_and_step: "jupiter:jupiter_details"
           leave_jupiter:
             ai_feedback:
               tokens_for_ai: "Onward!"
@@ -1352,9 +1372,10 @@ sections:
           - 'ganymede' if ganymede mentioned
           - 'callisto' if callisto mentioned
           - 'moon_menu' if they want the moon menu
-          - 'leave_jupiter' if leaving Jupiter, other planets
+          - 'back_to_planet' if they want to see Jupiter, back to jupiter, planet
+          - 'leave_jupiter' if leaving Jupiter entirely, other planets
           - 'stay' for questions about other moons
-        buckets: [io, europa, ganymede, callisto, moon_menu, leave_jupiter, stay]
+        buckets: [io, europa, ganymede, callisto, moon_menu, back_to_planet, leave_jupiter, stay]
         transitions:
           io:
             ai_feedback:
@@ -1376,6 +1397,10 @@ sections:
             ai_feedback:
               tokens_for_ai: "Back to moon selection!"
             next_section_and_step: "jupiter:jupiter_moon_menu"
+          back_to_planet:
+            ai_feedback:
+              tokens_for_ai: "Returning to Jupiter!"
+            next_section_and_step: "jupiter:jupiter_details"
           leave_jupiter:
             ai_feedback:
               tokens_for_ai: "Continuing your journey!"