M3: Asset pipeline — ContentPaths + ContentLoader + asset-test

Formalises Content/ access from the Godot host. Content lives at the
repo root (sibling of Theriapolis.Godot/), not duplicated under res://,
so the MonoGame branch and headless Tools keep reading from the same
single source of truth.

ContentPaths.cs:
  Static ContentRoot/DataDir/GfxDir resolved once via res:// walk-up
  and cached. Replaces two inline ResolveDataDir copies in SmokeTest
  and WorldMapView.

ContentLoader.cs:
  LoadGfx(relativePath) -> ImageTexture, cached by relative path.
  Bypasses the res:// import pipeline because Content/ lives outside
  the project — fine for static pixel-art assets at native size, and
  the project default texture filter is already Nearest. Cache is
  per-process, never evicted (full atlas <1 MB).

AssetTest.cs + Main.cs --asset-test flag:
  Smoke-tests the pipeline. Walks Content/Data and Content/Gfx,
  reports counts, attempts to load every PNG, prints per-subdir
  breakdown. Quits with non-zero on any failure.

Verified post-refactor (--asset-test):
  53 JSON files in Data, 50 PNG files in Gfx (8 tactical/deco +
  42 tactical/surface), 50/50 loaded, 0 failures.

Verified no regressions:
  --smoke-test (M1) still produces canonical FNV hashes.
  --world-map 12345 (M2) still produces 3 rivers / 91 roads /
  226 settlements / 0 rails / 0 bridges.

Scope note: plan mentioned "tile/NPC/CodexUI atlases — three
separate themes". Only tactical/ exists in Content/Gfx today; NPC
and CodexUI atlases never landed during MonoGame development. M3
ships what's actually present. ContentLoader.LoadGfx works for any
future sub-directories without changes.

Closes M3 of theriapolis-rpg-implementation-plan-godot-port.md.
Next: M4 (tactical render).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Theriapolis.Godot/Platform/AssetTest.cs

@@ -0,0 +1,78 @@
+using Godot;
+using System.IO;
+using System.Linq;
+
+namespace Theriapolis.GodotHost.Platform;
+
+/// <summary>
+/// M3 asset pipeline smoke test. Walks Content/Data and Content/Gfx,
+/// reports counts, and verifies every PNG under Gfx loads via
+/// ContentLoader. Exits non-zero on any failure.
+///
+/// Run with:
+///   godot --headless --path Theriapolis.Godot -- --asset-test
+/// </summary>
+public static class AssetTest
+{
+    public static int Run()
+    {
+        GD.Print($"[asset-test] Content root: {ContentPaths.ContentRoot}");
+        GD.Print($"[asset-test] Data dir:     {ContentPaths.DataDir}");
+        GD.Print($"[asset-test] Gfx dir:      {ContentPaths.GfxDir}");
+
+        if (!Directory.Exists(ContentPaths.DataDir))
+        {
+            GD.PrintErr($"[asset-test] FAIL: Data directory missing");
+            return 1;
+        }
+        if (!Directory.Exists(ContentPaths.GfxDir))
+        {
+            GD.PrintErr($"[asset-test] FAIL: Gfx directory missing");
+            return 1;
+        }
+
+        var jsonFiles = Directory.GetFiles(ContentPaths.DataDir, "*.json", SearchOption.AllDirectories);
+        GD.Print($"[asset-test] Data: {jsonFiles.Length} JSON files");
+
+        var pngFiles = Directory.GetFiles(ContentPaths.GfxDir, "*.png", SearchOption.AllDirectories);
+        GD.Print($"[asset-test] Gfx:  {pngFiles.Length} PNG files");
+
+        int loaded = 0;
+        int failed = 0;
+        foreach (var absolute in pngFiles)
+        {
+            string relative = Path.GetRelativePath(ContentPaths.GfxDir, absolute)
+                                  .Replace('\\', '/');
+            var tex = ContentLoader.LoadGfx(relative);
+            if (tex is null)
+            {
+                failed++;
+            }
+            else
+            {
+                loaded++;
+            }
+        }
+
+        GD.Print($"[asset-test] Loaded {loaded}/{pngFiles.Length} PNGs " +
+                 $"(cache size {ContentLoader.CacheCount}, failed {failed})");
+
+        if (failed > 0)
+        {
+            GD.PrintErr($"[asset-test] FAIL: {failed} texture(s) failed to load");
+            return 1;
+        }
+
+        // Also report the sub-tree breakdown, matching what M4 will care about
+        var bySubdir = pngFiles
+            .GroupBy(f => Path.GetRelativePath(ContentPaths.GfxDir, Path.GetDirectoryName(f)!)
+                              .Replace('\\', '/'))
+            .OrderBy(g => g.Key);
+        GD.Print($"[asset-test] PNG breakdown by sub-directory:");
+        foreach (var g in bySubdir)
+            GD.Print($"[asset-test]   {g.Key,-24} {g.Count(),3} files");
+
+        GD.Print($"[asset-test] OK");
+        return 0;
+    }
+}