Add black outline to alliance icon for terrain contrast (#4353)

## Problem

The green alliance icon above player names blends into similarly-colored
terrain — most notably irradiated land, which is the same green — making
it hard to spot allied players.

## Fix

Add a configurable dark outline to the alliance status icon, rendered in
the status-icon shader (the icons come from a pre-baked atlas with no
regeneration script, so this is done in-shader rather than by editing
the PNG).

- **Outline**: an alpha dilation gated to the alliance icon (slot 3).
8-direction sampling of the icon's alpha builds a black halo around its
silhouette; interior pixels and all other status icons are untouched.
- **No clipping**: the alliance icon's quad is grown outward into the
atlas cell's existing transparent padding so the halo isn't clipped at
the quad edge. The icon's on-screen size and position are unchanged; 8px
of the cell's 16px mipmap-safety padding is preserved.
- **Drain stays aligned**: the alliance-expiry drain effect's cut line
and faded-icon UVs are remapped into the expanded quad space so the
animation still lines up.
- **Tunable**: width is driven by `name.statusOutlineWidth` in
`render-settings.json` (default 6 texels; 0 disables), with a matching
"Status Outline Width" slider in the debug GUI.

## Testing

`tsc` and `eslint` pass. Verified in-game: the handshake now reads
clearly against irradiated terrain, with the outline rendering fully (no
edge clipping) and the drain animation still aligned.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/client/render/gl/render-settings.json

@@ -216,6 +216,7 @@
     "nameShadeBot": 0.4,
     "emojiRowOffset": 1.4,
     "statusRowOffset": 1.4,
+    "statusOutlineWidth": 6,
     "hoverFadeAlpha": 0.5,
     "hoverGlowWidth": 5,
     "hoverGlowAlpha": 0.75