docs: extract design philosophy, remove outdated spec

- Create docs/research/design-philosophy.md with:
  - Core design principles
  - Target audience
  - POD research findings
  - Preset rationale
  - Customisation philosophy
- Delete docs/spec.md (outdated, didn't match implementation)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/research/design-philosophy.md

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+# SimpleshopTheme Design Philosophy
+
+This document captures the design principles and research that informed the theme system architecture.
+
+## Core Principles
+
+1. **"One theme, infinite variations"** - Rather than offering multiple themes, we provide one solid foundation with curated customisation options
+2. **Constrained creativity** - Limit choices to prevent poor design outcomes while maintaining perceived variety
+3. **No professional photography required** - Defaults work well with product mockups, not just lifestyle imagery
+4. **Mobile-first** - All features work on touch devices (no hover-only interactions)
+5. **Ethical design** - No dark patterns like countdown timers or fake urgency
+
+## Target Audience
+
+- Solo POD creators (artists, illustrators, designers)
+- Small catalogs (typically <50 products)
+- Non-technical users who found WooCommerce too complex
+- Budget-conscious sellers
+
+## Research Findings: POD Theme Best Practices
+
+### What POD Sellers Actually Use
+- **Free themes dominate**: Dawn, Spotlight, Studio most popular on Shopify
+- **Premium choice**: Streamline ($350) best for growing POD brands
+- **Impulse** is fashion-focused, not ideal POD default
+
+### Key Requirements for POD
+1. Large product imagery (mockups need to shine)
+2. Clean/minimal design (products are the focus)
+3. Quick setup (non-technical users)
+4. Mobile-responsive (60%+ traffic)
+5. Works with small catalogs
+6. No reliance on lifestyle photography
+
+### What to Avoid
+- Countdown timers (dark pattern)
+- Complex promotional systems
+- Hover-only interactions
+- Features requiring professional photography
+- Enterprise complexity
+
+## Preset Design Rationale
+
+Each preset targets a specific aesthetic/use case:
+
+| Preset | Target Use Case |
+|--------|-----------------|
+| Gallery | Art galleries, editorial brands |
+| Studio | Default, versatile, works for most |
+| Boutique | Artisan, handmade goods |
+| Bold | Tech, contemporary, statement brands |
+| Playful | Fun, casual, approachable brands |
+| Minimal | Ultra-clean, luxury positioning |
+| Night | Premium, dramatic, dark mode lovers |
+| Classic | Traditional, established feel |
+
+## Customisation Philosophy
+
+### Parameters Exposed to Users
+- **Font pairing preset** - Enables brand expression without typography expertise
+- **Colour moods** - Warm/Cool/Neutral/Dark covers most brand needs
+- **Shape options** - Sharp/Soft/Round/Pill for personality
+- **Density** - Adjust spacing for catalog size
+- **Accent colours** - Primary brand customisation
+
+### Parameters Locked Down
+- **Line-height ratios** - Users break readability when exposed
+- **Letter-spacing** - Technical, easy to ruin
+- **Type scale ratio** - Mathematical harmony shouldn't be adjustable
+- **Mobile scaling** - Complex responsive logic
+
+The principle: expose choices that are hard to get wrong, lock down choices that require design expertise.
+
+## Combination Count
+
+With current options, the system offers:
+- 4 moods × 7 typographies × 4 shapes × 3 densities × 3 grids × 3 headers = **3,024 base combinations**
+- Plus accent colours, layout width, button styles, shadows, etc.
+
+This provides sufficient variety while keeping all combinations visually coherent.