Add feature/topic tags for improved snippet discoverability

- Add tags field to all 113 content YAML files with appropriate Java feature tags
  (records, sealed-classes, pattern-matching, switch, virtual-threads, streams,
  optional, collections, null-safety, text-blocks, var, concurrency, and more)
- Update content/template.json with tags field example
- Add html-generators/tags.properties mapping tag slugs to display names
- Add templates/topic-page.html template for topic listing pages
- Update templates/slug-template.html to render tag pills ({{tagPills}} token)
- Update templates/index-card.html to include data-tags attribute for filtering
- Update html-generators/generate.java to:
  - Parse tags from Snippet content
  - Include tags in snippets.json
  - Add data-tags attribute to index cards
  - Render tag pill links on snippet detail pages
  - Generate 43 topic pages at site/topics/{tag}.html
- Update site/styles.css with tag-pill and topic-badge styles
- Update site/app.js to show cards on topic pages and search by tags
- Update translations/strings/en.yaml with sections.tags and topics.* keys
- Update .gitignore to exclude site/topics/*.html (generated files)
- Update .github/workflows/deploy.yml to regenerate on tags.properties/categories.properties changes

Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Author: Copilot

.github/workflows/deploy.yml

@@ -10,6 +10,8 @@ on:
       - 'site/**'
       - 'html-generators/generateog.java'
       - 'html-generators/og/**'
+      - 'html-generators/tags.properties'
+      - 'html-generators/categories.properties'
   workflow_run:
     workflows: ['Build Generator JARs']
     types: [completed]
@@ -53,7 +55,7 @@ jobs:
 
             NEEDS_GENERATE=false
 
-            if echo "$CHANGED" | grep -qE '^(content/|translations/|templates/)'; then
+            if echo "$CHANGED" | grep -qE '^(content/|translations/|templates/|html-generators/tags\.properties|html-generators/categories\.properties)'; then
               NEEDS_GENERATE=true
             fi
 

.gitignore

@@ -11,6 +11,9 @@ site/security/*.html
 site/tooling/*.html
 site/enterprise/*.html
 
+# Generated topic pages (built by html-generators/)
+site/topics/*.html
+
 # Generated aggregate file (built from individual JSON sources by html-generators/)
 site/data/snippets.json
 

content/collections/collectors-teeing.yaml

@@ -46,6 +46,9 @@ related:
 - "collections/copying-collections-immutably"
 - "collections/unmodifiable-collectors"
 - "collections/stream-toarray-typed"
+tags:
+- streams
+- collectors
 docs:
 - title: "Collectors.teeing()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/stream/Collectors.html#teeing(java.util.stream.Collector,java.util.stream.Collector,java.util.function.BiFunction)"

content/collections/copying-collections-immutably.yaml

@@ -40,6 +40,8 @@ related:
 - "collections/immutable-set-creation"
 - "collections/map-entry-factory"
 - "collections/immutable-list-creation"
+tags:
+- collections
 docs:
 - title: "List.copyOf()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/List.html#copyOf(java.util.Collection)"

content/collections/immutable-list-creation.yaml

@@ -42,6 +42,8 @@ related:
 - "collections/immutable-map-creation"
 - "collections/immutable-set-creation"
 - "collections/sequenced-collections"
+tags:
+- collections
 docs:
 - title: "List.of()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/List.html#of()"

content/collections/immutable-map-creation.yaml

@@ -40,6 +40,8 @@ related:
 - "collections/copying-collections-immutably"
 - "collections/sequenced-collections"
 - "streams/stream-tolist"
+tags:
+- collections
 docs:
 - title: "Map.of()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Map.html#of()"

content/collections/immutable-set-creation.yaml

@@ -41,6 +41,8 @@ related:
 - "collections/copying-collections-immutably"
 - "collections/collectors-teeing"
 - "streams/stream-tolist"
+tags:
+- collections
 docs:
 - title: "Set.of()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Set.html#of()"

content/collections/map-entry-factory.yaml

@@ -38,6 +38,8 @@ related:
 - "collections/sequenced-collections"
 - "collections/immutable-map-creation"
 - "collections/immutable-list-creation"
+tags:
+- collections
 docs:
 - title: "Map.entry()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Map.html#entry(K,V)"

content/collections/reverse-list-iteration.yaml

@@ -43,6 +43,8 @@ related:
 - "collections/sequenced-collections"
 - "collections/immutable-list-creation"
 - "streams/stream-tolist"
+tags:
+- collections
 docs:
 - title: "SequencedCollection (Java 21)"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/SequencedCollection.html"

content/collections/sequenced-collections.yaml

@@ -42,6 +42,8 @@ related:
 - "collections/collectors-teeing"
 - "collections/immutable-set-creation"
 - "collections/immutable-map-creation"
+tags:
+- collections
 docs:
 - title: "Sequenced Collections (JEP 431)"
   href: "https://openjdk.org/jeps/431"