Add SwiftLint integration for code style enforcement

ios-spm-app-packaging/assets/templates/bootstrap/.swiftlint.yml

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+opt_in_rules:
+  - empty_count
+  - explicit_init
+  - sorted_imports
+  - redundant_nil_coalescing
+  - private_outlet
+  - overridden_super_call
+  - prohibited_super_call
+
+disabled_rules:
+  - trailing_whitespace
+
+analyzer_rules:
+  - explicit_self
+  - unused_import
+
+included:
+  - Sources
+
+excluded:
+  - .build
+  - build
+  - DerivedData
+  - Pods
+
+force_cast: warning
+force_try: error
+line_length:
+  warning: 120
+  error: 150
+type_body_length:
+  warning: 300
+  error: 500
+file_length:
+  warning: 500
+  error: 1000
+function_body_length:
+  warning: 40
+  error: 100
+
+reporter: "xcode"

ios-spm-app-packaging/references/swiftlint.md

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+# SwiftLint integration
+
+Enforces Swift code style. The bootstrap template includes a pre-configured `.swiftlint.yml`.
+
+## Install
+
+```bash
+brew install swiftlint
+```
+
+## Configuration
+
+The included `.swiftlint.yml` enforces:
+
+- Opt-in rules: `sorted_imports`, `empty_count`, `explicit_init`, `redundant_nil_coalescing`
+- Analyzer rules: `explicit_self`, `unused_import`
+- Line length: warning at 120, error at 150
+- Type/function body limits
+- `force_cast`: warning, `force_try`: error
+
+Customize by editing `.swiftlint.yml`.
+
+## Usage
+
+```bash
+swiftlint lint
+swiftlint lint --strict
+swiftlint autocorrect
+```
+
+## Xcode integration
+
+Add a Run Script Phase:
+
+```bash
+if which swiftlint >/dev/null; then
+  swiftlint
+else
+  echo "warning: SwiftLint not installed"
+fi
+```
+
+## Fastlane integration
+
+```ruby
+lane :lint do
+  swiftlint(mode: :lint, strict: true, reporter: "xcode")
+end
+```
+
+## CI integration
+
+```yaml
+- name: Lint
+  run: swiftlint lint --strict
+```