Add structure dots toggle to graphics settings (#4356)

## What

Adds an on/off **Structure dots** toggle to the graphics settings modal
(Structure Icons section), controlling whether structures collapse into
small dots when zoomed out.

## How

The renderer already gates the dots LOD on `structure.dotsZoomThreshold`
(structures become dots when `zoom <= threshold`). The debug GUI exposes
that threshold as a slider; this surfaces a simple player-facing toggle:

- `GraphicsOverrides.ts` — adds `structure.showDots` (boolean) to the
override schema.
- `RenderOverrides.ts` — when `showDots === false`,
`applyGraphicsOverrides` sets `dotsZoomThreshold = 0`. Since zoom is
always > 0, the dots LOD never triggers, so structures keep their full
icon at every zoom. When enabled (default), the threshold is left
untouched.
- `GraphicsSettingsModal.ts` — toggle button mirroring the existing
Classic icons / Classic level numbers toggles; defaults to On.
- `en.json` — `structure_dots_label` / `structure_dots_desc`.

The change applies live: a `settings.graphics` change re-runs
`applyGraphicsOverrides` onto the live settings object the passes read
each frame, and `dotsZoomThreshold` is a per-frame uniform.

## Testing

- `tsc --noEmit` clean.
- Verified in a headless solo game: the toggle renders (default On),
flipping it persists `structure.showDots = false`, and
`applyGraphicsOverrides` yields `dotsZoomThreshold` 1.2 when on / 0 when
off.

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

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

resources/lang/en.json

@@ -572,6 +572,8 @@
     "section_name_labels": "Name Labels",
     "section_structure_icons": "Structure Icons",
     "section_terrain": "Terrain",
+    "structure_dots_desc": "Collapse structure icons into small dots when zoomed out",
+    "structure_dots_label": "Structure dots",
     "territory_alpha_desc": "How opaque the territory fill is (lower lets terrain show through)",
     "territory_alpha_label": "Territory opacity",
     "territory_sat_desc": "How vivid the territory fill colors are (lower mutes them)",