feat: enhance admin ui with responsive design and ux improvements

- add podcast sidebar navigation
- add podcast dashboard with latest episodes
- add pagination to podcast episodes
- add components helper to reuse ui components (button, data_table, etc.)
- enhance podcast and episode forms by splitting them into form sections
- add hint tooltips to podcast and episode forms
- transform radio inputs as buttons for better ux
- replace explicit field by parental_advisory
- replace author field by publisher
- add podcasts_categories table to set multiple categories
- use choices.js to enhance multiselect fields
- update Language files
- update js dependencies to latest versions

closes #31, #9

app/Models/EpisodeModel.php

@@ -26,7 +26,7 @@ class EpisodeModel extends Model
         'enclosure_filesize',
         'description',
         'image_uri',
-        'explicit',
+        'parental_advisory',
         'number',
         'season_number',
         'type',
@@ -47,7 +47,6 @@ class EpisodeModel extends Model
         'slug' => 'required|regex_match[/^[a-zA-Z0-9\-]{1,191}$/]',
         'enclosure_uri' => 'required',
         'description' => 'required',
-        'image_uri' => 'required',
         'number' => 'is_natural_no_zero|permit_empty',
         'season_number' => 'is_natural_no_zero|permit_empty',
         'type' => 'required',