refactor: migrate plugins to Claude Code spec format

- Move plugin manifests from .github/plugin/ to .claude-plugin/
- Convert items[] to Claude Code spec fields (agents, commands, skills)
- Rename tags to keywords, drop display/featured/instructions from plugins
- Delete all symlinks and materialized files from plugin directories
- Add eng/materialize-plugins.mjs to copy source files into plugin dirs at publish time
- Add .github/workflows/publish.yml for staged->main publishing
- Update CI triggers to target staged branch
- Update validation, creation, marketplace, and README generation scripts
- Update CONTRIBUTING.md and AGENTS.md documentation
- Include all new content from main (polyglot-test-agent, gem-browser-tester,
  fabric-lakehouse, fluentui-blazor, quasi-coder, transloadit-media-processing,
  make-repo-contribution hardening, website logo/gradient changes)

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

plugins/java-development/.github/plugin/plugin.json

@@ -7,7 +7,7 @@
   },
   "repository": "https://github.com/github/awesome-copilot",
   "license": "MIT",
-  "tags": [
+  "keywords": [
     "java",
     "springboot",
     "quarkus",
@@ -15,58 +15,10 @@
     "junit",
     "javadoc"
   ],
-  "display": {
-    "ordering": "alpha",
-    "show_badge": false
-  },
-  "items": [
-    {
-      "path": "instructions/java.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/springboot.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/quarkus.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/quarkus-mcp-server-sse.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/convert-jpa-to-spring-data-cosmos.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/java-11-to-java-17-upgrade.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/java-17-to-java-21-upgrade.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "instructions/java-21-to-java-25-upgrade.instructions.md",
-      "kind": "instruction"
-    },
-    {
-      "path": "prompts/java-docs.prompt.md",
-      "kind": "prompt"
-    },
-    {
-      "path": "prompts/java-junit.prompt.md",
-      "kind": "prompt"
-    },
-    {
-      "path": "prompts/java-springboot.prompt.md",
-      "kind": "prompt"
-    },
-    {
-      "path": "prompts/create-spring-boot-java-project.prompt.md",
-      "kind": "prompt"
-    }
+  "commands": [
+    "./commands/java-docs.md",
+    "./commands/java-junit.md",
+    "./commands/java-springboot.md",
+    "./commands/create-spring-boot-java-project.md"
   ]
 }

plugins/java-development/commands/create-spring-boot-java-project.md

@@ -1 +0,0 @@
-../../../prompts/create-spring-boot-java-project.prompt.md

plugins/java-development/commands/java-docs.md

@@ -1 +0,0 @@
-../../../prompts/java-docs.prompt.md

plugins/java-development/commands/java-junit.md

@@ -1 +0,0 @@
-../../../prompts/java-junit.prompt.md

plugins/java-development/commands/java-springboot.md

@@ -1 +0,0 @@
-../../../prompts/java-springboot.prompt.md