Fix CI workflows: add required toolchain parameter to Rust installation steps

The dtolnay/rust-toolchain action requires an explicit 'toolchain' input parameter.
Added 'toolchain: stable' to all Rust toolchain installation steps in both
deploy-pr-preview.yml and build-test-push.yml workflows to resolve the
"'toolchain' is a required input" error that was causing lint jobs to fail.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: lmcdonough

.github/workflows/build-test-push.yml

@@ -33,6 +33,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: stable
           components: clippy, rustfmt
 
       - name: Use cached dependencies
@@ -60,6 +61,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: stable
           targets: x86_64-unknown-linux-gnu
 
       - name: Set OpenSSL Paths

.github/workflows/deploy-pr-preview.yml

@@ -63,6 +63,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: stable
           components: clippy, rustfmt
 
       - name: Use cached dependencies
@@ -92,6 +93,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@stable
         with:
+          toolchain: stable
           targets: x86_64-unknown-linux-gnu
 
       - name: Set OpenSSL Paths