Glow Garden

Build a tiny browser game called "Glow Garden".

Game spec
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A cozy night-garden idle clicker with no losing state. Click the dark soil (or move a dashed cursor with the arrow keys and press Space/Enter) to plant the selected seed; seeds grow over a fixed time scaled by upgrades, then begin dripping spores, the currency, per second. Three seed tiers — Firelily (0.8/s, cheap), Glowcap (4/s) and Lantern Fern (18/s) — are drawn as glowing procedural plants (petal ring, mushroom cap, arching lit fronds) that pulse in place and drift bioluminescent motes upward; per-plant cost rises 12% per purchase. The shop unlocks Glowcap and Lantern Fern behind one-time spore gates, and offers two repeatable upgrades: Richer Soil (+20% growth and drip speed) and Moonbeam (+50% spore yield), each multiplying its base cost by the difficulty curve. HUD shows current spores, spores/sec, and total earned, which is the score reported to the parent via postMessage. Difficulty sets starting spores (40/15/5), upgrade cost curve (1.12/1.28/1.5), and the tier-unlock gates, and the active level is shown top-right. Palette is deep indigo sky with twinkling stars, a crescent moon with a faint moonbeam shaft, and cyan/green bioluminescence.

Hard constraints — the game will be embedded in a sandboxed iframe on a static gallery site, and a headless browser will screenshot it:

1. Output exactly ONE self-contained HTML file. All CSS and JS inline. Zero external requests: no CDNs, no external fonts, images, or sounds, no fetch/XHR/WebSocket. Any sound must be synthesized with WebAudio.
2. The iframe sandbox is "allow-scripts allow-pointer-lock" (plus an autoplay permission). So: no localStorage, cookies, or indexedDB (opaque origin — access throws); no popups, window.open, or navigation; no access to the parent page; alert()/prompt()/confirm() are silently blocked.
3. The playfield must be visible within 800 ms of load — that is when the screenshot is taken. No dead white screen. If there is a start screen, make it visually rich.
4. Controls: keyboard AND mouse must both work, plus on-screen touch buttons for phones. Call preventDefault() on game keys (arrows, space) so the page never scrolls.
5. The view is 16:9 and must scale to fill the viewport with no overflow or scrollbars.
6. Show a visible score. If the genre has a losing state, show a game-over screen with a restart (button and a key). Idle/clicker games skip game over but still need clear numeric feedback.
7. If you track a score, report it to the arcade shell so the player's best is remembered between visits: on every score change, call parent.postMessage({ source: "ai-arcade", type: "score", score: <number> }, "*"). It is safe to call it no matter what the parent does with it.
8. Keep it tiny: aim for under 400 lines, 60 fps, no frameworks. That 400-line target does not apply to 3D games — true 3D (a camera and perspective-projected world) or pseudo-3D (projected road/track, depth-sorted sprites) — which need their own software renderer and typically land at 800–1400 lines. The rest of this constraint still binds every game: 60 fps, no frameworks, no external assets, and no padding to reach a length.
9. Difficulty: the arcade shell passes the player's chosen difficulty as a URL query parameter. Read it with new URLSearchParams(location.search).get("difficulty") — the value is "easy", "medium", or "hard" (missing or unknown means "medium"). Make the three levels meaningfully different — speed, lives, enemy pressure, reaction time, whatever fits the genre; clicker/idle games with no losing state use starting resources and upgrade cost curves instead. Show the active level in the HUD. Without the parameter the game must be fully playable at its default (medium) tuning.

Return only the complete HTML file, no commentary.