Add upgrade-deps skill for guided dependency upgrade workflow

.claude/skills/upgrade-deps/SKILL.md

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+---
+name: upgrade-deps
+description: Upgrade Gradle dependencies and Gradle wrapper version
+disable-model-invocation: true
+---
+
+# Dependency Upgrade Workflow
+
+This skill performs a full Gradle dependency upgrade for the Armeria project step by step.
+
+## Background: Minimum Java Version Per Module
+
+Armeria is a multi-module project with different minimum Java version requirements.
+Before upgrading a dependency, always verify that the new version supports the minimum
+Java version required by the modules that use it.
+
+| Java Version | Modules |
+|-------------|---------|
+| **8**  | `core`, `brave5`, `brave6`, `eureka`, `grpc`, `grpc-kotlin`, `graphql-protocol`, `jetty9`, `junit4`, `junit5`, `kafka`, `kotlin`, `logback`, `logback12`, `logback13`, `micrometer-context`, `oauth2`, `prometheus1`, `protobuf`, `reactor3`, `resteasy`, `retrofit2`, `rxjava2`, `rxjava3`, `sangria`, `scala*`, `spring:boot2-*`, `dropwizard2`, `thrift0.9`–`thrift0.17`, `tomcat8`, `tomcat9`, `xds`, `zookeeper3`, `saml`, `bucket4j`, `consul`, `nacos` |
+| **11** | `athenz`, `graphql`, `jetty10`, `jetty11`, `kubernetes`, `logback14`, `thrift0.18`–`thrift0.22`, `tomcat10` |
+| **17** | `ai:mcp`, `jetty12`, `resilience4j2`, `spring:boot3-*`, `spring:spring6`, `spring:boot4-*`, `spring:spring7` |
+
+When in doubt, check `settings.gradle` for the `java`, `java11`, or `java17` flag on each subproject.
+
+## Step 1: Run dependencyUpdates
+
+```
+./gradlew dependencyUpdates
+```
+
+The report is saved to `build/dependencyUpdates/report.txt`.
+
+## Step 2: Parse the Report
+
+Read `build/dependencyUpdates/report.txt` to identify all outdated dependencies.
+For each dependency, note the current version and the available latest version.
+
+If a version looks ambiguous (unexpected format, major version bump, unusual naming),
+verify on Maven Central before proceeding:
+  https://central.sonatype.com/artifact/{groupId}/{artifactId}
+
+## Step 3: Check Java Version Compatibility
+
+For each candidate upgrade:
+1. Find which modules use this dependency in `dependencies.toml`
+2. Determine the minimum Java version required by those modules (see table above)
+3. Check the new library version's minimum Java requirement (Maven Central / release notes)
+4. If the library's required Java > module's minimum Java → **skip the upgrade**
+5. If compatible → proceed with the upgrade
+
+## Step 4: Update dependencies.toml
+
+Edit the `[versions]` section in `dependencies.toml` to update the version strings.
+The file is located at the root of the repository: `dependencies.toml`.
+
+## Step 5: Upgrade Gradle Wrapper
+
+Check the latest stable Gradle release at https://gradle.org/releases/ and update
+`gradle/wrapper/gradle-wrapper.properties`:
+
+```properties
+distributionUrl=https\://services.gradle.org/distributions/gradle-X.Y.Z-all.zip
+```
+
+## Step 6: Verify the Build
+
+Run the full build including tests to catch both compilation errors and runtime regressions:
+
+```
+./gradlew build --no-daemon
+```
+
+If there are compilation errors, API breaking changes, or test failures caused by the upgrade,
+fix them before proceeding.
+
+## Step 7: Commit
+
+Create a commit with the **exact** message format below. Follow it strictly — do not add extra
+sections, reorder bullets, or change the structure:
+
+```
+Update dependencies
+
+- {library-name} {old-version} -> {new-version}
+- {library-name} {old-version} -> {new-version}
+- Build
+   - {library-name} {old-version} -> {new-version}
+   - {library-name} {old-version} -> {new-version}
+```
+
+Rules:
+- Each production dependency (api/implementation scope) gets one bullet: `- {name} {old} -> {new}`
+- The `- Build` bullet groups build-only dependencies (testImplementation, annotationProcessor,
+  relocated libs, non-transitive deps); nest them as sub-bullets with 3-space indent
+- Use the exact library name as it appears in `dependencies.toml` (the version key name)
+- Sort entries **alphabetically (A → Z)** within each section
+- Omit skipped dependencies from the commit message entirely
+- If no build-only deps were upgraded, omit the `- Build` section entirely
+
+Example:
+```
+Update dependencies
+
+- grpc-java 1.63.0 -> 1.64.0
+- jackson 2.17.0 -> 2.18.0
+- Build
+   - checkstyle 10.14.0 -> 10.17.0
+   - errorprone 2.27.0 -> 2.28.0
+```