Add backend support for Hydra mount (#15482)

* chore: update time travelers shop to display seasonal backgrounds

* chore: update time travelers banner (note CSS borken rn)

* chore: fix borken CSS and update logic in shop

* chore: added isSubscribed function, not working

* chore: isSubscribed working but no bg for subscribers

* chore: logic and css updates

* chore: update habitica-images

* chore: add check for trinket

* chore: more time traveler shop logicking

* Add backend support for Hydra mount

- Add Dragon-Hydra to special mounts in stable.js
  - Configure as contributor level 7 reward with canFind: true
  - Add GIF format support for mount sprites
  - Enable admin panel granting capability

* Fix Vue template errors in timeTravelers component

* Fix duplicate template block in timeTravelers component

* add CSS for Hydra mount GIF sprites

Added CSS rules for Mount_Head_Dragon-Hydra and Mount_Body_Dragon-Hydra GIF sprites

* Remove the separate Hydra mount dimension declaration

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Co-authored-by: CuriousMagpie <eilatan@gmail.com>

website/common/script/content/stable.js

@@ -115,6 +115,7 @@ const canFindSpecial = {
     'Hippogriff-Hopeful': true,
 
     // Contributor/Backer pets
+    'Dragon-Hydra': true, // Contributor level 7
     'LionCub-Ethereal': false, // Backer tier 90
     'Jackalope-RoyalPurple': true, // subscription
     'Gryphon-Gryphatrice': false, // Pet once granted to kickstarter
@@ -152,6 +153,7 @@ const specialPets = {
 
 const specialMounts = {
   'BearCub-Polar': 'polarBear',
+  'Dragon-Hydra': 'hydra',
   'LionCub-Ethereal': 'etherealLion',
   'MantisShrimp-Base': 'mantisShrimp',
   'Turkey-Base': 'turkey',