docs: add design spec for configurable icons from Docker share

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/superpowers/specs/2026-04-14-configurable-icons-design.md

@@ -0,0 +1,59 @@
+# Configurable Icons from Docker Share
+
+**Date:** 2026-04-14  
+**Status:** Approved
+
+## Problem
+
+Icons for shifts are currently PNG files bundled in the repository under `Client/wwwroot/icons/`. This means adding or changing an icon requires a code change and a redeployment. The user wants icons to be configurable at runtime, placed on the same Docker-mounted volume as monthly schedule files and other configuration.
+
+## Solution
+
+Serve icon files from `config/icons/` (a subfolder of the existing Docker share) using ASP.NET Core's static file middleware with a `PhysicalFileProvider`. No frontend changes are required — the URL path `/icons/filename.png` stays identical.
+
+## Architecture
+
+### Server change (`Server/Program.cs`)
+
+Add a second `UseStaticFiles` call after the existing one:
+
+```csharp
+var iconsPath = Path.Combine(Directory.GetCurrentDirectory(), "config", "icons");
+Directory.CreateDirectory(iconsPath);
+app.UseStaticFiles(new StaticFileOptions
+{
+    FileProvider = new PhysicalFileProvider(iconsPath),
+    RequestPath = "/icons"
+});
+```
+
+- `config/icons/` is created automatically on first run if absent.
+- Files placed there are served at `/icons/{filename}` immediately, no restart needed.
+- Built-in ASP.NET Core static file serving provides ETags, cache headers, and range request support.
+
+### Cleanup
+
+- Delete `Client/wwwroot/icons/` and all PNG files within it.
+- Remove all `<Content Update="wwwroot\icons\*.png">` entries from `Client/ShiftScheduler.Client.csproj`.
+
+### No changes needed
+
+- `Shift.IsPngIcon` computed property
+- `Shift.Icon` field
+- `<img src="icons\@shift.Icon">` in `Index.razor`
+- `ConfigurationDialog.razor`
+- Any other frontend or shared model code
+
+## Data Flow
+
+1. User places `myicon.png` in `config/icons/` on the Docker share.
+2. In `appsettings.json` (or `config/shifts.json`), the shift's `Icon` field is set to `myicon.png`.
+3. The Blazor client fetches shift config from `GET /api/shift/shifts`.
+4. `Shift.IsPngIcon` returns `true`, and the UI renders `<img src="icons/myicon.png">`.
+5. The browser GETs `/icons/myicon.png` — served by the `PhysicalFileProvider` from `config/icons/myicon.png`.
+
+## Out of Scope
+
+- Emoji icons are unaffected.
+- No upload UI for icons — files are placed on the share directly (consistent with how schedule files work).
+- No fallback to repo-bundled icons (repo icons are removed entirely).