feat(ci): implement semver release channels

- Rename dev-release.yml → alpha-release.yml
- Alpha builds: v0.0.4-alpha.{run_number} (prerelease)
- Add pr-build.yml for draft releases
- PR builds: v0.0.4-pr.{num}.bid.{id} (draft, not published)
- Add attestation permissions for SLSA compliance
- No more deleting/recreating dev tag

Versioning strategy:
- Draft: +pr.{NUM}.bid.{ID} (testable, not published)
- Alpha: -alpha.{N} (canary channel)
- Beta: -beta (quality scored)
- RC: -rc.{N} (release candidate)
- Stable: no suffix

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/alpha-release.yml

@@ -1,4 +1,4 @@
-name: Dev Release
+name: Alpha Release
 
 on:
   push:
@@ -7,9 +7,12 @@ on:
 
 permissions:
   contents: write
+  id-token: write
+  attestations: write
 
 env:
-  CORE_VERSION: dev
+  # Next version - update when releasing
+  NEXT_VERSION: "0.0.4"
 
 jobs:
   build:
@@ -55,34 +58,37 @@ jobs:
           cp dist/* release/ 2>/dev/null || true
           ls -la release/
 
-      - name: Delete existing dev release
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: gh release delete dev -y || true
-
-      - name: Delete existing dev tag
-        run: git push origin :refs/tags/dev || true
-
-      - name: Create dev release
+      - name: Create alpha release
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          gh release create dev \
-            --title "Development Build" \
-            --notes "Latest development build from the dev branch.
+          VERSION="v${{ env.NEXT_VERSION }}-alpha.${{ github.run_number }}"
 
+          gh release create "$VERSION" \
+            --title "Alpha: $VERSION" \
+            --notes "Canary build from dev branch.
+
+          **Version:** $VERSION
           **Commit:** ${{ github.sha }}
           **Built:** $(date -u +'%Y-%m-%d %H:%M:%S UTC')
+          **Run:** ${{ github.run_id }}
+
+          ## Channel: Alpha (Canary)
+
+          This is an automated pre-release for early testing.
+
+          - Systems and early adopters can test breaking changes
+          - Quality scoring determines promotion to beta
+          - Use stable releases for production
 
           ## Installation
 
           \`\`\`bash
           # macOS/Linux
-          curl -fsSL https://github.com/host-uk/core/releases/download/dev/core-linux-amd64 -o core
+          curl -fsSL https://github.com/host-uk/core/releases/download/$VERSION/core-linux-amd64 -o core
           chmod +x core && sudo mv core /usr/local/bin/
           \`\`\`
-
-          This is a pre-release for testing. Use tagged releases for production." \
+          " \
             --prerelease \
             --target dev \
             release/*

.github/workflows/pr-build.yml

@@ -0,0 +1,100 @@
+name: PR Build
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+  workflow_dispatch:
+    inputs:
+      pr_number:
+        description: 'PR number to build'
+        required: true
+        type: number
+
+permissions:
+  contents: write
+  pull-requests: read
+
+env:
+  # Next version - update when releasing
+  NEXT_VERSION: "0.0.4"
+
+jobs:
+  build:
+    # Only build if PR is from the same repo (not forks) or manually triggered
+    if: github.event.pull_request.head.repo.full_name == github.repository || github.event_name == 'workflow_dispatch'
+    strategy:
+      matrix:
+        include:
+          - os: ubuntu-latest
+            platform: linux/amd64
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+
+      - name: Build
+        uses: host-uk/build@dev
+        with:
+          build-name: core
+          build-platform: ${{ matrix.platform }}
+          build: true
+          package: true
+          sign: false
+
+  draft-release:
+    needs: build
+    runs-on: ubuntu-latest
+    env:
+      # Safe: PR number is numeric, not user-controlled string
+      PR_NUM: ${{ github.event.pull_request.number || inputs.pr_number }}
+      PR_SHA: ${{ github.event.pull_request.head.sha || github.sha }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Download artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: dist
+          merge-multiple: true
+
+      - name: Prepare release files
+        run: |
+          mkdir -p release
+          cp dist/* release/ 2>/dev/null || true
+          ls -la release/
+
+      - name: Create draft release
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Build metadata uses + which is valid semver but GitHub tags encode it
+          VERSION="v${{ env.NEXT_VERSION }}+pr.${PR_NUM}.bid.${{ github.run_id }}"
+          # GitHub tags can't have + so we use a different format for the tag
+          TAG="v${{ env.NEXT_VERSION }}-pr.${PR_NUM}.bid.${{ github.run_id }}"
+
+          # Delete existing draft for this PR if it exists
+          gh release delete "$TAG" -y 2>/dev/null || true
+          git push origin ":refs/tags/$TAG" 2>/dev/null || true
+
+          gh release create "$TAG" \
+            --title "Draft: PR #${PR_NUM}" \
+            --notes "Draft build for PR #${PR_NUM}.
+
+          **Version:** $VERSION
+          **Tag:** $TAG
+          **PR:** #${PR_NUM}
+          **Commit:** ${PR_SHA}
+          **Built:** $(date -u +'%Y-%m-%d %H:%M:%S UTC')
+          **Run:** ${{ github.run_id }}
+
+          ## Channel: Draft
+
+          This is a draft build for testing PR changes before merge.
+          Not intended for production use.
+
+          Build artifacts available for download and testing.
+          " \
+            --draft \
+            --prerelease \
+            release/*