Add extended traits, project config, and setup plugin

[obj-p]

Summary

Three complementary features that give developers the fidelity of running their app with the nimbleness of SwiftUI previews — eliminating the need for micro apps / dev apps.

• Extended traits: locale, layoutDirection, legibilityWeight added to preview_configure and preview_start, with new variant presets (rtl, ltr, boldText). Empty string clears a trait. Locale injection validated against code injection. Layout direction and legibility weight validated against enum sets.
• Project config (.previewsmcp.json): auto-discovered config file for platform, device, trait defaults, and quality. Precedence: explicit param > config > default. Gives AI agents project intent without inference.
• Setup plugin (PreviewsSetupKit): protocol-based system replacing micro apps. setUp() runs once per session (outside hot-reload path) for SDK init, auth, fonts, DI container setup. wrap() runs every render for theme providers and environment values. PreviewsMCP builds the setup package independently via SetupBuilder — the user's app target has zero dependency on PreviewsMCP. Trait modifiers applied outside wrap so explicit overrides always win.

Architecture

.previewsmcp.json (setup.packagePath → PreviewSetup/)
        │
        ▼
SetupBuilder ──swift build──► PreviewSetup/.build/
        │                          ├── Modules/ToDoPreviewSetup.swiftmodule
        │                          └── libToDoPreviewSetup.a (archived by SetupBuilder)
        ▼
BridgeGenerator ──── import ToDoPreviewSetup ────► bridge.dylib
        │               @_cdecl("previewSetUp")      │
        │               ToDoPreviewSetup.wrap()       │
        ▼                                             ▼
    Host app calls previewSetUp once ──► createPreviewView on every reload

The user's app Package.swift is completely untouched. Setup works across SPM, Xcode, and Bazel.

Changes

• Phase 1: Extended traits — 3 new properties, validation (including injection prevention), presets, .environment() modifiers, MCP schemas, CLI flags
• Phase 2: Project config — ProjectConfig type + ProjectConfigLoader, MCP/CLI integration with --config flag, quality field used in snapshot/variants
• Phase 3: Setup plugin — PreviewsSetupKit library, SetupBuilder (builds setup package, archives .o → .a, extracts compiler flags), @_cdecl("previewSetUp") with async bridge, hasCalledSetUp in both host apps, full pipeline wiring
• Phase 4: Documentation — CLAUDE.md + README.md updated
• Phase 5: Example — shared .previewsmcp.json at examples/, standalone PreviewSetup/ package with observable state + preview banner, tested across all 4 build systems
• Security fixes: locale injection prevention, setup identifier validation
• Review fixes: trait clearing via empty string, config quality wiring, MCP schema enum constraints

Test coverage

• 67 unit tests passing (55 trait/setup + 10 config + 2 security)
• Integration tested across SPM, xcodeproj, xcworkspace, Bazel with setup plugin active

Test plan

• swift test --filter BridgeGeneratorTraitsTests — 57 tests for traits + setup code gen + security
• swift test --filter ProjectConfigTests — 10 tests for config decoding + directory walking
• All 4 example projects render with setup banner (spm, xcodeproj, xcworkspace, bazel)
• Trait variants (light/dark/rtl/boldText) produce correct snapshots
• Dark + RTL traits compose correctly with setup wrapper
• Empty-string trait clearing works
• Locale injection rejected (quotes, backslashes, newlines)
• Invalid setup identifiers rejected (non-Swift-identifier characters)

🤖 Generated with Claude Code