ci(ff): support feature freeze automation

RELEASE.md

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+# Release Process
+
+Quick reference for running elastic-agent releases using mage automation.
+
+## Prerequisites
+
+```bash
+# Install mage (if not already installed)
+go install github.com/magefile/mage@latest
+
+# Configure environment
+export CURRENT_RELEASE="9.5.0"
+export GITHUB_TOKEN="ghp_your_token_here"
+```
+
+## Major/Minor Release
+
+### Automated (Recommended)
+
+```bash
+# Dry run first
+export CURRENT_RELEASE="9.5.0"
+export GITHUB_TOKEN="ghp_..."
+export DRY_RUN=true
+mage release:runMajorMinor
+
+# Review changes, then run for real
+export DRY_RUN=false
+git checkout main && git pull origin main
+mage release:runMajorMinor
+```
+
+### Manual Steps
+
+```bash
+# 1. Start clean
+git checkout main && git pull origin main
+
+# 2. Prepare release files
+mage release:prepareMajorMinor
+
+# 3. Review changes
+git diff
+
+# 4. Create release branch and commit
+mage release:createBranch
+
+# 5. Push branch
+git push origin 9.5
+
+# 6. Create pull request
+mage release:createPR
+```
+
+## Patch Release
+
+### Automated (Recommended)
+
+```bash
+# Dry run first
+export CURRENT_RELEASE="9.4.1"
+export BASE_BRANCH="9.4"
+export GITHUB_TOKEN="ghp_..."
+export DRY_RUN=true
+git checkout 9.4 && git pull origin 9.4
+mage release:runPatch
+
+# Review changes, then run for real
+export DRY_RUN=false
+mage release:runPatch
+```
+
+### Manual Steps
+
+```bash
+# 1. Checkout release branch
+export CURRENT_RELEASE="9.4.1"
+export BASE_BRANCH="9.4"
+git checkout 9.4 && git pull origin 9.4
+
+# 2. Update files
+mage release:updateVersion 9.4.1
+mage release:updateDocs 9.4.1
+
+# 3. Commit and push
+git add -A
+git commit -m "[Release] Prepare patch release 9.4.1"
+git push origin 9.4
+```
+
+## Individual Commands
+
+```bash
+# Update version only
+mage release:updateVersion 9.5.0
+
+# Update docs only
+mage release:updateDocs 9.5.0
+
+# Update mergify only
+mage release:updateMergify 9.5.0
+
+# See all release commands
+mage -l | grep release
+```
+
+## Environment Variables
+
+| Variable | Required | Default | Description |
+|----------|----------|---------|-------------|
+| `CURRENT_RELEASE` | ✓ | - | Version to release (e.g., `9.5.0`) |
+| `GITHUB_TOKEN` | ✓ | - | GitHub personal access token |
+| `DRY_RUN` | | `false` | Preview mode (set to `true` to skip push/PR) |
+| `BASE_BRANCH` | | `main` | Base branch for PRs |
+| `PROJECT_OWNER` | | `elastic` | GitHub repository owner |
+| `PROJECT_REPO` | | `elastic-agent` | Repository name |
+
+## Troubleshooting
+
+**"CURRENT_RELEASE environment variable not set"**
+```bash
+export CURRENT_RELEASE="9.5.0"
+```
+
+**"GITHUB_TOKEN environment variable not set"**
+```bash
+# Create token at: https://github.com/settings/tokens
+export GITHUB_TOKEN="ghp_..."
+```
+
+**"failed to create branch: reference already exists"**
+```bash
+# Delete existing branch
+git branch -D 9.5
+# Or checkout existing branch
+git checkout 9.5
+```
+
+## Full Documentation
+
+For detailed documentation, see [dev-tools/mage/release/README.md](dev-tools/mage/release/README.md)
+
+## Help
+
+- **Issues**: https://github.com/elastic/elastic-agent/issues
+- **Slack**: #ingest-team
+- **Migration Plan**: [specs/MIGRATION_PLAN_ELASTIC_AGENT.md](specs/MIGRATION_PLAN_ELASTIC_AGENT.md)