refactor: remove Thymeleaf UI, consolidate to React SPA

Remove the legacy Thymeleaf+HTMX UI at /ui to consolidate on the React
SPA at /. This removes ExplorerController, all Thymeleaf templates,
htmx/alpine static assets, the explorer-tailwind config, and the
spring-boot-starter-thymeleaf Maven dependency.

- Delete ExplorerController.java and ExplorerControllerTest.java
- Delete src/main/resources/templates/ (10 HTML files)
- Delete htmx.min.js and alpine.min.js from static/js/
- Remove spring-boot-starter-thymeleaf from pom.xml
- Delete explorer-tailwind.config.ts and build:explorer-css script
- All 1440 tests pass, clean package build verified

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Author: aksOps

pom.xml

@@ -57,10 +57,6 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-cache</artifactId>
         </dependency>
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-thymeleaf</artifactId>
-        </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-actuator</artifactId>

src/main/frontend/explorer-tailwind.config.ts

@@ -5,8 +5,7 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
-    "build": "tsc -b && vite build && npm run build:explorer-css",
-    "build:explorer-css": "npx tailwindcss -c ./explorer-tailwind.config.ts -i ./src/explorer.css -o ../resources/static/css/explorer.css --minify",
+    "build": "tsc -b && vite build",
     "preview": "vite preview"
   },
   "dependencies": {