fix: add CI (ubuntu+macos matrix) + wire POLYLANE_CYCLE so ledger gates work

Conversation self-audit found two concrete holes:
- No CI on a public repo with 446 tests (run only manually -> rot). Add GitHub
  Actions running shellcheck + tests/run.sh on a ubuntu+macOS MATRIX — macOS (BSD
  coreutils) catches the class of bug the corpus head -n 0 fix just addressed, which
  GNU/ubuntu silently accepts.
- The runner's ledger row used ${POLYLANE_CYCLE:-0} but the SKILL launch never
  exported POLYLANE_CYCLE -> every row was cycle=0 -> ledger trend/roi (which compare
  consecutive cycles) silently no-op'd. Export POLYLANE_CYCLE=<N> at launch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: GHGuide

.github/workflows/ci.yml

@@ -0,0 +1,29 @@
+name: ci
+on:
+  push:
+    branches: [main]
+  pull_request:
+jobs:
+  test:
+    # matrix over BOTH coreutils families — macOS (BSD) catches bugs like the
+    # `head -n 0` corpus bug that GNU/ubuntu silently accepts.
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install deps (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y jq shellcheck tmux
+      - name: Install deps (macOS)
+        if: runner.os == 'macOS'
+        run: brew install jq shellcheck tmux
+      - name: Shellcheck all helpers
+        run: |
+          rc=0
+          for f in bin/*.sh; do shellcheck -S warning "$f" || rc=1; done
+          exit $rc
+      - name: Run the test suite
+        run: tests/run.sh

SKILL.md

@@ -311,7 +311,7 @@ with `--resume` (DONE lanes skipped), drains safe approval prompts itself (so a
 runner no longer blocks lanes), parks+notifies critical ones, and writes a heartbeat:
 ```
 BIN="$(dirname "$(command -v polylane-run.sh || echo "$HOME/.claude/skills/polylane/bin/x")")"
-POLYLANE_SESSION="polylane-c<N>" "$BIN/polylane-supervisor.sh" .polylane/run.json
+POLYLANE_CYCLE=<N> POLYLANE_SESSION="polylane-c<N>" "$BIN/polylane-supervisor.sh" .polylane/run.json
 ```
 Print the tmux watch commands in chat (`tmux attach -t polylane-c<N>`), then wait
 for the finish notification. **Read run state through the state surface, never by