feat: add Cursor, Codex, and OpenCode harnesses — maximize every AI coding tool

- AGENTS.md: universal cross-tool file read by Claude Code, Cursor, Codex, and OpenCode
- .cursor/: 15 hook events via hooks.json, 16 hook scripts with DRY adapter pattern,
  29 rules (9 common + 20 language-specific) with Cursor YAML frontmatter
- .codex/: reference config.toml, Codex-specific AGENTS.md supplement,
  10 skills ported to .agents/skills/ with openai.yaml metadata
- .opencode/: 3 new tools (format-code, lint-check, git-summary), 3 new hooks
  (shell.env, experimental.session.compacting, permission.ask), expanded instructions,
  version bumped to 1.6.0
- README: fixed Cursor section, added Codex section, added cross-tool parity table
- install.sh: now copies hooks.json + hooks/ for --target cursor

.cursor/rules/swift-coding-style.md

@@ -0,0 +1,47 @@
+---
+description: "Swift coding style extending common rules"
+globs: ["**/*.swift", "**/Package.swift"]
+alwaysApply: false
+---
+# Swift Coding Style
+
+> This file extends the common coding style rule with Swift specific content.
+
+## Formatting
+
+- **SwiftFormat** for auto-formatting, **SwiftLint** for style enforcement
+- `swift-format` is bundled with Xcode 16+ as an alternative
+
+## Immutability
+
+- Prefer `let` over `var` -- define everything as `let` and only change to `var` if the compiler requires it
+- Use `struct` with value semantics by default; use `class` only when identity or reference semantics are needed
+
+## Naming
+
+Follow [Apple API Design Guidelines](https://www.swift.org/documentation/api-design-guidelines/):
+
+- Clarity at the point of use -- omit needless words
+- Name methods and properties for their roles, not their types
+- Use `static let` for constants over global constants
+
+## Error Handling
+
+Use typed throws (Swift 6+) and pattern matching:
+
+```swift
+func load(id: String) throws(LoadError) -> Item {
+    guard let data = try? read(from: path) else {
+        throw .fileNotFound(id)
+    }
+    return try decode(data)
+}
+```
+
+## Concurrency
+
+Enable Swift 6 strict concurrency checking. Prefer:
+
+- `Sendable` value types for data crossing isolation boundaries
+- Actors for shared mutable state
+- Structured concurrency (`async let`, `TaskGroup`) over unstructured `Task {}`