feat(shorebird_cli): add --public-key-cmd and --sign-cmd support (#3605)

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build Commands
+
+```bash
+# Run all tests (must run from packages/ directory to avoid cache conflicts)
+cd packages && very_good test -r
+
+# Run tests for a single package (can use -r failures-only to reduce output)
+dart test packages/shorebird_cli
+```
+
+## Architecture
+
+Dart monorepo. Main package is `shorebird_cli`.
+
+**Platform-specific operations** use the Releaser/Patcher pattern:
+- `commands/release/` - `Releaser` base class with platform implementations
+- `commands/patch/` - `Patcher` base class with platform implementations
+
+**Dependency injection** uses `scoped_deps` with zone-based refs (see any `*Ref` variable).
+
+## Code Style
+
+- PR titles must follow semantic commit format (enforced in CI)
+- CSpell: use inline `// cspell:words` for 1-2 files; add to global config for more
+- Prefer new commits over amending in PRs - history gets squashed anyway