Add Advanced 3D Sample 1621 (AI Navigation Demo)

Author: DavidQ

docs/dev/CODEX_COMMANDS.md

@@ -1,3 +1,3 @@
 MODEL: GPT-5.3-codex
 REASONING: high
-COMMAND: Implement samples 1618-1620, integrate into index, ensure visible camera movement and UI clarity, package to <project folder>/tmp/BUILD_PR_LEVEL_17_30_ADVANCED_3D_SAMPLES_BATCH_4.zip
+COMMAND: Implement sample 1621 AI navigation demo with visible pathing, integrate into samples/index.html, package to <project folder>/tmp/BUILD_PR_LEVEL_17_31_ADVANCED_3D_SAMPLES_BATCH_5.zip

docs/dev/COMMIT_COMMENT.txt

@@ -1 +1 @@
-Add Advanced 3D Samples batch 4 (1618-1620)
+Add Advanced 3D Sample 1621 (AI Navigation Demo)

docs/dev/reports/validation_checklist.txt

@@ -1,3 +1,3 @@
-- [ ] samples load
-- [ ] UI visible
-- [ ] no errors
+- [ ] sample loads
+- [ ] agents move
+- [ ] paths visible

docs/pr/BUILD_PR_LEVEL_17_31_ADVANCED_3D_SAMPLES_BATCH_5.md

@@ -0,0 +1,9 @@
+# BUILD_PR_LEVEL_17_31_ADVANCED_3D_SAMPLES_BATCH_5
+
+Implement:
+- samples/1621-ai-navigation
+
+Requirements:
+- pathfinding visible
+- agents move correctly
+- debug visualization optional

docs/pr/PLAN_PR_LEVEL_17_31_ADVANCED_3D_SAMPLES_BATCH_5.md

@@ -0,0 +1,7 @@
+# PLAN_PR_LEVEL_17_31_ADVANCED_3D_SAMPLES_BATCH_5
+
+Purpose:
+Complete Advanced 3D Samples.
+
+Scope:
+- 1621 AI Navigation Demo

samples/index.html

@@ -493,6 +493,7 @@ <h2>Phase 16 - 3D Capability Track</h2>
         <a class="live" href="./phase-16/1618/index.html" title="Examines moving light behavior against multiple material swatches with visible camera orbit motion." data-tags="camera3d, lighting3d, materials3d, render3d, scene, themetokens" data-primary="lighting-materials-lab">Sample 1618 - Lighting & Materials Lab</a>
         <a class="live" href="./phase-16/1619/index.html" title="Demonstrates a readable debug HUD layered above an active 3D scene with explicit world/UI labels." data-tags="camera3d, debughud3d, ui-overlay, render3d, scene, themetokens" data-primary="debug-hud-sample">Sample 1619 - Debug HUD Sample</a>
         <a class="live" href="./phase-16/1620/index.html" title="Provides a compact 3D pickup mini game reference with follow camera movement and clear HUD scoring." data-tags="camera3d, minigame3d, pickups, hud, scene, themetokens" data-primary="mini-game-reference">Sample 1620 - Mini Game (3D Reference)</a>
+        <a class="live" href="./phase-16/1621/index.html" title="Demonstrates visible AI pathfinding routes and movement across a blocked 3D navigation grid." data-tags="camera3d, ai3d, pathfinding, navigation, scene, themetokens" data-primary="ai-navigation-demo">Sample 1621 - AI Navigation Demo</a>
       </div>
     </section>    
   </div>