fix(ci): maturin manifest-path is Cargo.toml not pyproject.toml

maturin>=1.5 requires -m to point to Cargo.toml, not pyproject.toml.
Fixes wheel build job failure in CI (all three matrix targets).
Also switches to manifest-path: action param for cleaner workflow syntax.
Applies same fix to Makefile build-wheel and develop targets.

.github/workflows/rust.yml

@@ -72,7 +72,8 @@ jobs:
         uses: PyO3/maturin-action@v1
         with:
           command: build
-          args: --release -m crates/headroom-py/pyproject.toml --out dist
+          manifest-path: crates/headroom-py/Cargo.toml
+          args: --release --out dist
           target: ${{ matrix.maturin-target }}
       - name: Upload wheel artifact
         uses: actions/upload-artifact@v4

Makefile

@@ -29,7 +29,7 @@ test-parity:
 		echo "error: activate a venv first (e.g. source .venv/bin/activate)"; \
 		exit 1; \
 	fi
-	$(MATURIN) develop -m crates/headroom-py/pyproject.toml
+	$(MATURIN) develop -m crates/headroom-py/Cargo.toml
 	$(CARGO) run -p headroom-parity -- run --fixtures $(FIXTURES)
 
 bench:
@@ -43,7 +43,7 @@ build-proxy:
 	printf 'headroom-proxy: %s bytes (%.1f MiB)\n' "$$SIZE" "$$(echo "$$SIZE / 1048576" | bc -l)"
 
 build-wheel:
-	$(MATURIN) build --release -m crates/headroom-py/pyproject.toml
+	$(MATURIN) build --release -m crates/headroom-py/Cargo.toml
 
 fmt:
 	$(CARGO) fmt --all