feat: add Figma-native export functionality

[findyourexit]

FigGit v0.3.0 – Figma-Native Export Bundle

Unified Export Bundles

• Introduced ExportBundle to normalize all export outputs, so UI, diffing, and commits consume a single structure regardless of format (buildExportBundle.ts, types/export.ts, messaging/context/plugin updates).
• Persisted per-file hashes to avoid redundant commits when documents remain unchanged.

Figma-Native Export Pipeline

• Added buildFigmaNativeExport with deterministic metadata, per-collection splitting, slugged filenames, alias resolution, and valueNormalization utilities.
• Created reusable helpers (path.ts, slugify.ts, VariableModeValue relocation) and comprehensive tests (figmaNativeExport.test.ts).

GitHub Commit Improvements

• New multi-file commitFiles workflow batches updates, reuses embedded contentHash detection, and skips files already matching remote content.
• Plugin commit flow now uses bundle metadata for smarter commit messages and settings persistence.

UI/UX Enhancements

• Settings tab gains ExportOptionsDisclosure so users choose DTCG vs Figma-native and single vs per-collection outputs.
• StatusSummary, JsonViewer, and DiffViewer surface per-document metadata, copy actions, and multi-file diffs with remote error handling.

Docs & Packaging

• README now explains both schemas with example Figma-native JSON and revised distribution instructions.
• Manifest gains dev-mode capability, dependencies upgraded (esbuild 0.25), and PLUGIN_VERSION constant set to 0.3.0.