Add migration guide and skill entry for javax to jakarta transition (#1537)

* Add migration guide from javax to jakarta namespace

This document provides a comprehensive guide for migrating Java code from the javax namespace to the jakarta namespace, including steps for scanning, updating dependencies, and verifying the migration.

* Add javax to jakarta migration skill entry

skills/javax-to-jakarta-migration/SKILL.md

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+---
+name: javax-to-jakarta-migration
+description: "Migrate Java code from javax.* to jakarta.* namespace. Use when upgrading to Tomcat 11, Jakarta EE 10, or when javax imports are detected in the codebase."
+argument-hint: "File, package, or module to migrate"
+---
+
+# javax → jakarta Migration Skill
+
+## When to Use
+- Upgrading to Tomcat 11 / Jakarta EE 10+
+- Code review detects `javax.*` imports
+- Migrating an existing project to the jakarta namespace
+
+## Procedure
+
+### Step 1 — Scan for javax Usage
+Search the codebase for all `javax.*` imports that need migration:
+```
+javax.servlet.*      → jakarta.servlet.*
+javax.persistence.*  → jakarta.persistence.*
+javax.validation.*   → jakarta.validation.*
+javax.annotation.*   → jakarta.annotation.*
+javax.inject.*       → jakarta.inject.*
+javax.enterprise.*   → jakarta.enterprise.*
+javax.faces.*        → jakarta.faces.*
+javax.ws.rs.*        → jakarta.ws.rs.*
+javax.el.*           → jakarta.el.*
+javax.json.*         → jakarta.json.*
+javax.mail.*         → jakarta.mail.*
+javax.websocket.*    → jakarta.websocket.*
+```
+
+**Do NOT migrate** these (they remain in `javax.*`):
+- `javax.sql.*` — part of JDK
+- `javax.naming.*` — part of JDK (JNDI)
+- `javax.crypto.*` — part of JDK
+- `javax.net.*` — part of JDK
+- `javax.security.auth.*` — part of JDK
+- `javax.swing.*`, `javax.xml.parsers.*` — JDK packages
+
+### Step 2 — Update pom.xml
+Replace dependency coordinates:
+
+| Old | New |
+|-----|-----|
+| `javax.servlet:javax.servlet-api` | `jakarta.servlet:jakarta.servlet-api:6.0.0` |
+| `javax.persistence:javax.persistence-api` | `jakarta.persistence:jakarta.persistence-api:3.1.0` |
+| `javax.validation:validation-api` | `jakarta.validation:jakarta.validation-api:3.0.2` |
+| `javax.annotation:javax.annotation-api` | `jakarta.annotation:jakarta.annotation-api:2.1.1` |
+
+### Step 3 — Update web.xml (if present)
+```xml
+<!-- Old namespace -->
+<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" version="4.0">
+
+<!-- New namespace -->
+<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee" version="6.0">
+```
+
+### Step 4 — Update Java Source Files
+Replace all `javax.` imports with `jakarta.` equivalents in `.java` files.
+
+### Step 5 — Verify
+1. Run `mvn clean compile` or `gradlew build` — fix any compilation errors
+2. Run `mvn test` or `gradlew test` — ensure all tests pass
+3. Search for any remaining `javax.*` imports (excluding JDK packages)
+
+### Output
+Provide a migration summary listing all files changed, imports replaced, and any manual steps required.