Add 90s web whimsy: clipart decorations across all pages

- Add img/ folder with 224 transparent PNG clipart illustrations
- Add CSS classes for clipart placement (.clipart, .clipart-left,
  .clipart-right, .clipart-section, .clipart-divider, .clipart-wide,
  .clipart-inline) with hover rotation effect and responsive rules
- Decorate all 7 content pages + index + about with themed clipart:
  section headers, floating side images, wide section dividers,
  fact-box icons, and home page card icons
- Add AGENTS.md with project conventions and constraints

AGENTS.md

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+# AGENTS.md
+
+## What this is
+
+Static HTML/CSS/JS website. No build tools, no npm, no frameworks, no templating. Every page is a standalone `.html` file at the root, sharing `css/style.css` and `js/main.js`.
+
+## Core constraints
+
+- **Factual accuracy is critical.** All real-world claims (dates, numbers, patent numbers, scientific facts) must be verifiable. When adding or editing content, verify specific claims — especially patent numbers, statistics, and historical details. Past sessions found 80+ factual errors across pages; assume any new content carries the same risk.
+- **`about.html` contains fictional lore** (site "founded in 1999 by librarian Marguerite Calef"). This is intentional. Do not "correct" it.
+- **Background must be `#ffffff`** (pure white), not cream or off-white. The owner has clipart/images that float on white backgrounds and look wrong on any other color.
+- **No comments in code** unless explicitly requested.
+
+## Style / aesthetic
+
+Late-90s/early-2000s "hidden gem" website styled like a DK reference book:
+- Georgia / Times New Roman serif fonts
+- Images with drop shadows (`box-shadow`)
+- Colored section bars (each topic has a distinct color)
+- Fake visitor counter (localStorage-based), "Best viewed at 1024×768" footer, "Last updated" timestamp
+- Konami code easter egg, double-click title reveals hidden text (`<span class="easter-egg">`), console tips
+- **Clipart decorations** — transparent PNGs from `img/` folder placed whimsically throughout articles using CSS classes: `.clipart` (centered), `.clipart-left` / `.clipart-right` (floating beside text), `.clipart-section` (top of page), `.clipart-divider` (between sections), `.clipart-inline` (within text). Clipart should feel like 90s web decoration — small, scattered, thematically matched to article content.
+
+## Known issues
+
+- **Saluting Device patent (US 656,278, 1900)** on `inventions.html` was NOT verified. It may be incorrect. Check Google Patents before assuming it's real.
+
+## Page structure
+
+| File | Topic | Body class |
+|---|---|---|
+| `index.html` | Home / card grid | (none) |
+| `natural-world.html` | Forests, oceans, symbiosis, extremophiles | `section-natural-world` |
+| `inventions.html` | Accidental inventions, printing press, strange patents | `section-inventions` |
+| `phenomena.html` | Ball lightning, placebo, synesthesia, Mpemba effect | `section-phenomena` |
+| `maps.html` | Cartography, phantom islands, Tristan da Cunha, Derinkuyu | `section-maps` |
+| `human-body.html` | Brain, gut, skeleton, eye, blood, phantom limbs | `section-human-body` |
+| `space.html` | Universe scale, neutron stars, dark matter, Voyager | `section-space` |
+| `about.html` | Fictional site lore | `section-about` |
+
+## Development
+
+No build or serve command needed — open any `.html` file directly in a browser. For local dev with live reload, any static server works (`python3 -m http.server`, etc.).
+
+No tests, no linting, no CI.