ci: fix workflow_dispatch releasing into the void

The release workflow happily accepts a manual dispatch with any tag
string, then passes it to git log and softprops/action-gh-release
without ever checking if the tag actually *exists* as a git ref.
Confusion ensues — changelog generation silently produces garbage
and the release gets created pointing at nothing useful.

Add a tag validation step that fails fast with a clear error before
any downstream jobs run. Since both build and release already depend
on the changelog job via `needs`, this acts as a proper gate.

While at it, add --all-features to the CI build and test steps so
feature-gated code actually gets compiled and tested, not just
linted by clippy. Having clippy check code that never gets built
is the kind of false confidence that bites you on release day.

.github/workflows/ci.yml

@@ -42,6 +42,6 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
-      - run: cargo build --workspace
+      - run: cargo build --workspace --all-features
       - run: cargo check --no-default-features --workspace
-      - run: cargo test --workspace
+      - run: cargo test --workspace --all-features

.github/workflows/release.yml

@@ -26,6 +26,14 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
+      - name: Validate tag exists
+        env:
+          RELEASE_TAG: ${{ inputs.tag || github.ref_name }}
+        run: |
+          if ! git rev-parse "${RELEASE_TAG}" >/dev/null 2>&1; then
+            echo "::error::Tag ${RELEASE_TAG} does not exist in the repository"
+            exit 1
+          fi
       - name: Generate changelog
         id: changelog
         env: