docs: update handbook for atmosphere polish and brochure site

docs/HANDBOOK.md

@@ -1,6 +1,6 @@
 # Darkwatch Handbook
 
-**Last updated:** 2026-04-12
+**Last updated:** 2026-04-11
 
 A reference for everyone working on or with Darkwatch — whether you're a DM discovering the tool, a developer joining the project, or a collaborator adding features.
 
@@ -84,11 +84,12 @@ Each character has a luck token toggle. Players and the DM can both see and togg
 
 The DM can layer atmosphere effects that all players see in real time:
 
-- **Fog** — a dark gradient overlay with adjustable intensity
-- **Fire** — Three.js particle simulation, full screen
-- **Rain / Embers** — tsParticles overlay
+- **Fog** — drifting radial-gradient layers with adjustable intensity; fades in smoothly when enabled
+- **Fire** — Three.js GLSL shader with a realistic colour ramp (deep red tips → orange → amber → warm yellow core), per-column height variation for a ragged silhouette, and ember glow at the base
+- **Rain** — translucent blue-white drops that increase in density with intensity; at high intensity the angle tilts slightly, simulating wind-driven rain
+- **Embers** — small slow-drifting sparks with flickering opacity; more numerous and finer than rain
 
-Atmosphere is DM-only to control; all players see the active effects.
+Each effect has an independent intensity slider. Atmosphere is DM-only to control; all players see the active effects.
 
 ### Initiative Tracker
 
@@ -121,7 +122,7 @@ Features currently planned or in progress:
 - **Snow atmosphere effect** — tsParticles, evaluating after DM feedback on existing effects
 - **Ambient audio** — optional background sound; low priority
 
-Longer-term ideas: multi-system support (Cairn, Knave, Cyberpunk RED), profile image uploads, metrics and analytics, API documentation, and a public marketing site.
+Longer-term ideas: multi-system support (Cairn, Knave, Cyberpunk RED), profile image uploads, metrics and analytics, and API documentation.
 
 ## Known limitations
 
@@ -222,6 +223,12 @@ shadowdark/
 │   │   ├── types.ts          # Shared TypeScript types
 │   │   └── socket.ts         # Socket.IO singleton
 │   └── public/               # Static assets (dice themes, etc.)
+├── site/                     # Static marketing brochure (no build step)
+│   ├── index.html            # Single-page brochure
+│   ├── style.css             # All brochure styles
+│   ├── main.js               # Smooth scroll + hero parallax
+│   ├── screenshots.js        # Playwright script — regenerates screenshots
+│   └── assets/screenshots/   # Committed PNGs used by the brochure
 ├── server/
 │   ├── src/
 │   │   ├── routes/           # Express REST routes + socket handler files