Add generate.py to build HTML pages from JSON snippets

Python script reads category/*.json files and generates HTML detail pages
using a consistent template. Replaces hand-crafted HTML with generated output.

Main content sections are identical to originals. Related card sections
now use canonical JSON data instead of hand-edited snippets, fixing
stale code examples and inconsistent labels.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: brunoborges

concurrency/completablefuture-chaining.html

@@ -227,7 +227,7 @@ <h3>Stable values</h3>
 }</pre>
             </div>
             <div class="card-code-layer modern-layer">
-              <div class="mini-label">Java 25</div>
+              <div class="mini-label">Java 25 (Preview)</div>
               <pre class="code-text">private final StableValue&lt;Logger&gt; logger =
     StableValue.of(this::createLogger);
 
@@ -302,7 +302,7 @@ <h3>Structured concurrency</h3>
 } finally { exec.shutdown(); }</pre>
             </div>
             <div class="card-code-layer modern-layer">
-              <div class="mini-label">Java 25</div>
+              <div class="mini-label">Java 25 (Preview)</div>
               <pre class="code-text">try (var scope = new StructuredTaskScope
         .ShutdownOnFailure()) {
     var u = scope.fork(this::fetchUser);

concurrency/concurrent-http-virtual.html

@@ -232,7 +232,7 @@ <h3>Structured concurrency</h3>
 } finally { exec.shutdown(); }</pre>
             </div>
             <div class="card-code-layer modern-layer">
-              <div class="mini-label">Java 25</div>
+              <div class="mini-label">Java 25 (Preview)</div>
               <pre class="code-text">try (var scope = new StructuredTaskScope
         .ShutdownOnFailure()) {
     var u = scope.fork(this::fetchUser);
@@ -273,7 +273,7 @@ <h3>Stable values</h3>
 }</pre>
             </div>
             <div class="card-code-layer modern-layer">
-              <div class="mini-label">Java 25</div>
+              <div class="mini-label">Java 25 (Preview)</div>
               <pre class="code-text">private final StableValue&lt;Logger&gt; logger =
     StableValue.of(this::createLogger);
 
@@ -315,7 +315,7 @@ <h3>Lock-free lazy initialization</h3>
 }</pre>
             </div>
             <div class="card-code-layer modern-layer">
-              <div class="mini-label">Java 25</div>
+              <div class="mini-label">Java 25 (Preview)</div>
               <pre class="code-text">class Config {
     private static final
         StableValue&lt;Config&gt; INST =

concurrency/lock-free-lazy-init.html

@@ -343,4 +343,4 @@ <h3>Scoped values</h3>
 
   <script src="../app.js"></script>
 </body>
-</html>
+</html>

concurrency/scoped-values.html

@@ -338,4 +338,4 @@ <h3>Stable values</h3>
 
   <script src="../app.js"></script>
 </body>
-</html>
+</html>

concurrency/stable-values.html

@@ -338,4 +338,4 @@ <h3>Scoped values</h3>
 
   <script src="../app.js"></script>
 </body>
-</html>
+</html>

concurrency/structured-concurrency.html

@@ -338,4 +338,4 @@ <h3>Stable values</h3>
 
   <script src="../app.js"></script>
 </body>
-</html>
+</html>

concurrency/thread-sleep-duration.html

@@ -229,7 +229,7 @@ <h3>Stable values</h3>
 }</pre>
             </div>
             <div class="card-code-layer modern-layer">
-              <div class="mini-label">Java 25</div>
+              <div class="mini-label">Java 25 (Preview)</div>
               <pre class="code-text">private final StableValue&lt;Logger&gt; logger =
     StableValue.of(this::createLogger);