feat: add PyPI publishing workflow and readme metadata

- Add readme = "README.md" to pyproject.toml for PyPI project description
- Add manual publish-pypi.yml workflow using trusted publishers (OIDC)
- Update release.yml install instructions to prefer PyPI

The publish workflow is manually triggered after a release, checks out the
specified tag, verifies version consistency, builds with uv, and publishes
using trusted publishing (no API tokens required).

Prerequisites before first use:
- Take ownership of the specify-cli PyPI project (#2908)
- Create a 'pypi' environment in repo settings
- Configure trusted publisher on PyPI for this repo/workflow

Closes #2908

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/publish-pypi.yml

@@ -0,0 +1,70 @@
+name: Publish to PyPI
+
+on:
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Release tag to publish (e.g., v0.10.1)'
+        required: true
+        type: string
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout release tag
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+        with:
+          ref: ${{ inputs.tag }}
+
+      - name: Verify tag is a release
+        run: |
+          TAG="${{ inputs.tag }}"
+          if [[ ! "$TAG" =~ ^v[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+            echo "Error: '$TAG' is not a valid release tag (expected vX.Y.Z)"
+            exit 1
+          fi
+
+      - name: Verify tag matches package version
+        run: |
+          TAG_VERSION="${{ inputs.tag }}"
+          TAG_VERSION="${TAG_VERSION#v}"
+          PROJECT_VERSION="$(python3 -c 'import tomllib; print(tomllib.load(open("pyproject.toml","rb"))["project"]["version"])')"
+          if [[ "$TAG_VERSION" != "$PROJECT_VERSION" ]]; then
+            echo "Error: Tag version ($TAG_VERSION) does not match pyproject.toml version ($PROJECT_VERSION)"
+            exit 1
+          fi
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5
+
+      - name: Build package
+        run: uv build
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
+        with:
+          name: dist
+          path: dist/
+
+  publish:
+    needs: build
+    runs-on: ubuntu-latest
+    environment: pypi
+    permissions:
+      id-token: write
+    steps:
+      - name: Download build artifacts
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
+        with:
+          name: dist
+          path: dist/
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5
+
+      - name: Publish to PyPI
+        run: uv publish --trusted-publishing always

.github/workflows/release.yml

@@ -66,10 +66,16 @@ jobs:
           ## Install
 
           \`\`\`bash
-          uv tool install specify-cli --from git+https://github.com/github/spec-kit.git@${VERSION}
+          uv tool install specify-cli@latest
           specify init my-project
           \`\`\`
 
+          Or install from source:
+
+          \`\`\`bash
+          uv tool install specify-cli --from git+https://github.com/github/spec-kit.git@${VERSION}
+          \`\`\`
+
           NOTES_EOF
 
           echo "## What's Changed" >> release_notes.md