docs(release): add semantic changelog automation

.github/workflows/release.yml

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+name: Release
+
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  issues: write
+  pull-requests: write
+
+jobs:
+  semantic-release:
+    name: Semantic release
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      - name: Generate release
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: >
+          npx -y
+          -p semantic-release@25.0.3
+          -p @semantic-release/changelog@6.0.3
+          -p @semantic-release/commit-analyzer@13.0.1
+          -p @semantic-release/git@10.0.1
+          -p @semantic-release/github@12.0.8
+          -p @semantic-release/release-notes-generator@14.1.1
+          semantic-release

.releaserc.json

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+{
+  "branches": ["main"],
+  "tagFormat": "v${version}",
+  "plugins": [
+    "@semantic-release/commit-analyzer",
+    "@semantic-release/release-notes-generator",
+    [
+      "@semantic-release/changelog",
+      {
+        "changelogFile": "CHANGELOG.md"
+      }
+    ],
+    [
+      "@semantic-release/git",
+      {
+        "assets": ["CHANGELOG.md"],
+        "message": "chore(release): ${nextRelease.version} [skip ci]\n\n${nextRelease.notes}"
+      }
+    ],
+    "@semantic-release/github"
+  ]
+}

CHANGELOG.md

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+# Changelog
+
+Release notes are generated by semantic-release from conventional commits.

docs/release-management.md

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+# Release management
+
+Metrix uses semantic-release to generate root versions, GitHub releases, and
+`CHANGELOG.md` entries from conventional commits.
+
+## CI command
+
+The Release workflow runs semantic-release through `npx -p ...` so release
+tooling does not add root dependency or lockfile churn.
+
+## Flow
+
+1. Use conventional commit subjects such as `fix(api): ...`,
+   `feat(bot): ...`, and `docs(web): ...`.
+2. Merge to `main`.
+3. The Release workflow runs semantic-release, updates `CHANGELOG.md`, commits
+   release notes, and creates the Git tag.
+
+No npm publish step is configured because this repository currently keeps its
+packages private.