chore: add bump-and-release workflow (#30)

Adds a manually triggered workflow that bumps the version in
pyproject.toml, commits, creates an annotated tag, and pushes —
reducing a release to a single step via the GitHub UI or CLI.

Closes #29

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: stedrew

.github/workflows/bump-and-release.yml

@@ -0,0 +1,48 @@
+name: Bump and Release
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: "Version to release (semver, e.g. 1.2.3)"
+        required: true
+
+permissions:
+  contents: write  # push commit + tag → triggers release.yml
+
+jobs:
+  bump-and-tag:
+    name: Bump version, tag, and push
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # full history so tag checks are accurate
+
+      - name: Validate semver format
+        run: |
+          if ! echo "${{ inputs.version }}" | grep -qE '^[0-9]+\.[0-9]+\.[0-9]+$'; then
+            echo "::error::Version must be semver (e.g. 1.2.3). Got: ${{ inputs.version }}"
+            exit 1
+          fi
+
+      - name: Fail if tag already exists
+        run: |
+          if git tag | grep -q "^v${{ inputs.version }}$"; then
+            echo "::error::Tag v${{ inputs.version }} already exists."
+            exit 1
+          fi
+
+      - name: Bump version in pyproject.toml
+        run: |
+          sed -i 's/^version = ".*"/version = "${{ inputs.version }}"/' pyproject.toml
+
+      - name: Commit, tag, and push
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add pyproject.toml
+          git commit -m "chore: bump version to ${{ inputs.version }}"
+          git tag -a "v${{ inputs.version }}" -m "Release v${{ inputs.version }}"
+          git push origin main --follow-tags