👷 ci: Add GitHub Actions build and smoke test pipeline

This project has had no automated testing or CI for its entire history.
As a code-preservation project, manual play-testing was the only way to
verify changes didn't break the game. This commit adds a GitHub Actions
pipeline that proves compilation succeeds and the game starts correctly
on every push and pull request.

The pipeline tests with both GCC and Clang via a build matrix, catching
compiler-specific issues in parallel. The Makefile defaults to
`-ltermcap` which is unavailable as a standalone library on the CI
runner; the workflow overrides with `LIBS="-lncurses"` which provides
termcap compatibility through `ncurses`.

A smoke test pipes LOOK, QUIT, Y into the game and asserts the welcome
banner, opening room description, and clean exit message all appear.
This catches initialization failures, data file corruption, and command
loop regressions without modifying any game source.

Compilation caching via `ccache` keeps repeat builds fast. Each compiler
gets its own cache keyed on source file content hashes, with prefix-
based restore, so a single changed file still benefits from cached
results for the other 32 compilation units. Concurrency controls cancel
in-progress runs when new commits land on the same ref.

No game source files are modified — the CI infrastructure is entirely
additive and lives in `.github/`.

Assisted-by: Claude Opus 4.6 (1M context)
Signed-off-by: Justin Wheeler <jwheel@fedoraproject.org>

Author: justwheel

.github/workflows/ci.yml

@@ -0,0 +1,51 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        cc: [gcc, clang]
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Restore compiler cache
+        uses: actions/cache@v5
+        with:
+          path: ~/.cache/ccache
+          key: ccache-${{ matrix.cc }}-${{ hashFiles('*.c', '*.h', 'Makefile') }}
+          restore-keys: |
+            ccache-${{ matrix.cc }}-
+
+      - name: Install dependencies
+        run: sudo apt-get update -qq && sudo apt-get install -y -qq libncurses-dev ccache
+
+      - name: Build
+        run: |
+          ccache --zero-stats
+          make clean
+          make CC="ccache ${{ matrix.cc }}" LIBS="-lncurses" -j$(nproc)
+          ccache --show-stats
+
+      - name: Verify binary
+        run: test -x ./zork
+
+      - name: Smoke test
+        run: |
+          output=$(printf "LOOK\nQUIT\nY\n" | timeout 10 ./zork 2>&1)
+          echo "$output"
+          echo "--- Verifying expected output ---"
+          echo "$output" | grep -q "Welcome to Dungeon"
+          echo "$output" | grep -q "white house"
+          echo "$output" | grep -q "mailbox"
+          echo "$output" | grep -q "game is over"
+          echo "--- Smoke test passed ---"