ci: Swatinem rust-cache; buildx gha cache for docker

.gitea/workflows/ci.yml

@@ -22,15 +22,10 @@ jobs:
         with:
           components: rustfmt, clippy
 
+      # Caches ~/.cargo registry/git and target/, keyed on toolchain + Cargo.lock;
+      # prunes workspace-crate artifacts so the cache holds only compiled deps.
       - name: Cache cargo
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            target
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
-          restore-keys: ${{ runner.os }}-cargo-
+        uses: Swatinem/rust-cache@v2
 
       - name: fmt
         run: cargo fmt --all -- --check
@@ -38,6 +33,7 @@ jobs:
       - name: clippy
         run: cargo clippy --workspace --all-targets -- -D warnings
 
+      # --workspace covers tui (it is outside default-members).
       - name: test
         run: cargo test --workspace