docs: add sanctum-web layout redesign spec

docs/superpowers/specs/2026-04-22-sanctum-web-layout-redesign.md

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+# sanctum-web Layout Redesign
+
+**Date:** 2026-04-22  
+**Repo:** git.mithraic.cloud/ad3laid3/sanctum-web  
+**Base:** stoatchat/for-web (Solid.js + Vite + TypeScript)
+
+---
+
+## Goal
+
+Fork the Stoat web frontend and fix its layout proportions so the app feels native on desktop and works properly as a PWA. The message area should dominate the screen. Nothing in the API, auth, or business logic layer is changed.
+
+---
+
+## Layout
+
+The root shell is rebuilt as a four-column CSS Grid:
+
+```
+[server icons 65px] [channels 240px] [messages 1fr] [members 240px]
+```
+
+| Panel | Width | Behaviour |
+|---|---|---|
+| Server icon sidebar | 65px fixed | Icon-only, scrollable, always visible |
+| Channel list | 240px default | User-resizable, collapsible |
+| Message area | fills remaining space (1fr) | Message list + pinned input at bottom |
+| Member list | 240px | Collapsible, hidden by default on narrow viewports |
+
+---
+
+## Scope
+
+**Changed:**
+- Root layout shell component — CSS replaced with proper grid
+- Global CSS spacing/sizing tokens that cause proportion issues
+
+**Not changed:**
+- API client
+- WebSocket layer
+- Auth flow
+- Message rendering components
+- Channel/server/member components
+- Any business logic
+
+---
+
+## Build & Deployment
+
+- Repo: `git.mithraic.cloud/ad3laid3/sanctum-web`
+- CI: Forgejo Actions — `pnpm build` on push to `main`, rsync `dist/` to VPS
+- Serves at: `mithraic.space/app` (replaces current for-web output, no Caddy changes)
+- Sanctum desktop app picks up the new frontend automatically on next launch
+
+---
+
+## Out of Scope
+
+- Tauri desktop wrapper (separate project, builds on this frontend)
+- Feature additions beyond layout fixes
+- Mobile/responsive breakpoints beyond basic collapse behaviour
+- Rebranding (keep existing Stoat/Revolt dark aesthetic)