feat: bootstrap design kit and vaporwave demo baseline

kit/patterns/import-export/README.md

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+# Import / Export Pattern
+
+Canonical file transfer UX patterns for Go web applications:
+
+- file import forms (CSV/JSON and similar)
+- validation preview tables before confirm
+- confirm step with human-readable summary
+- export controls (format + scope + options)
+- predictable file download behavior and filenames
+
+This pattern covers UI and UX contracts. Business-specific validation and file schemas remain in
+the host project's own architecture docs.
+

kit/patterns/import-export/contract.md

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+# Contract: Import / Export Workflows
+
+## Import Workflow
+
+Recommended stages:
+
+1. `Upload`
+2. `Preview / Validate`
+3. `Confirm`
+4. `Execute`
+5. `Result summary`
+
+Rules:
+
+- Validation preview must be human-readable (table/list), not raw JSON only.
+- Warnings and errors should be shown per row and in aggregate summary.
+- Confirm step should clearly communicate scope and side effects.
+
+## Export Workflow
+
+- User must explicitly choose export scope (`selected`, `filtered`, `all`) when ambiguity exists.
+- Export format should be explicit (`csv`, `json`, etc.).
+- Download response should set:
+  - `Content-Type`
+  - `Content-Disposition`
+- If CSV targets spreadsheet users, document delimiter and BOM policy.
+
+## Error Handling
+
+- Import errors should map to clear user-facing messages.
+- Export errors after streaming starts must degrade gracefully (human-readable fallback).
+