feat(selection): port retail polygon picking and vivid marker

Replace the projected Setup-sphere rectangle and independent physics-wall ray with retail's render-coupled picker: only visible server-object parts participate, each exact drawing sphere broad-phases the camera-eye ray, and first-in-DAT-order visual polygon hits globally outrank sphere fallbacks.

Replace the devtools-only procedural triangles with the retained gameplay VividTargetIndicator using retail client-enum surfaces 1..4, radar-blip colorization, Setup selection-sphere framing, and the exact eight-pixel viewport clamp.

Release build succeeds with zero warnings and all 5,886 tests pass with five intentional skips.

Co-authored-by: OpenAI Codex <codex@openai.com>

docs/research/2026-07-17-retail-world-selection-pseudocode.md

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+# Retail world selection and vivid target indicator
+
+Oracle: September 2013 EoR named retail client. Cross-checks: the extracted
+WorldBuilder mesh path (DAT geometry and current part transforms) and ACE object
+identity/qualities. Neither reference implementation supplies the client picker;
+the named retail functions below are authoritative.
+
+## Mouse selection
+
+`SmartBox::find_object @ 0x00451C60`
+
+```text
+remember the clicked viewport pixel
+clear the previous per-frame selection accumulator
+arm mouse selection for the next world draw
+```
+
+`CPhysicsPart::Draw @ 0x0050D7A0`, `RenderDeviceD3D::DrawMesh @ 0x005A0860`,
+and `Render::GfxObjUnderSelectionRay @ 0x0054C740`
+
+```text
+for each physics part which reaches the normal visible-mesh draw path:
+    reject parts which do not belong to a server object
+    transform the one world selection ray into this part's local coordinates
+    divide by the part's GfxObj scale (do not change the ray parameter units)
+
+    sphere = gfxObj.drawing_sphere
+    if sphere does not intersect the local ray:
+        continue
+
+    if a polygon has already won globally and sphereDistance is farther:
+        continue
+
+    if sphereDistance is nearer than the current sphere fallback:
+        remember this object's id, part index, and sphereDistance
+
+    for polygons in the GfxObj's stored flat DAT order:
+        if polygon_hits_ray(polygon, localRay, out t):
+            remember only this FIRST polygon hit for this part
+            if t is nearer than the current global polygon winner:
+                remember this object's id, part index, and t
+            break
+```
+
+`CPolygon::polygon_hits_ray @ 0x005395E0`
+
+```text
+if polygon.sides_type == ST_SINGLE (raw value 0)
+and dot(ray.direction, polygon.plane.normal) > 0:
+    miss                         // back face
+
+denominator = dot(ray.direction, polygon.plane.normal)
+if abs(denominator) < 0.0002:
+    miss                         // parallel to the plane
+
+t = plane/ray intersection time
+if t < 0:
+    miss                         // behind the viewer
+
+point = ray.origin + t * ray.direction
+normal = normalize(sum(cross(vertex[i] - vertex[0],
+                             vertex[i+1] - vertex[0])))
+for each ordered edge (previous -> current):
+    inward = cross(normal, current - previous)
+    if dot(point - previous, inward) < 0:
+        miss
+return hit
+```
+
+The broad-phase helper is retail `CSphere::sphere_intersects_ray @
+0x005377A0`: it rejects rays beginning in/on the sphere, requires squared ray
+direction length at least `0.0002`, solves the quadratic in double precision,
+and chooses the near root when non-negative or the far root otherwise.
+The ray origin is `Render::viewpoint` (the camera eye), not the unprojected
+near-plane point; `Render::pick_ray @ 0x0054B610` supplies only its direction.
+
+`Render::GetMouseSelectionObjectID @ 0x0054C950`
+
+```text
+if any polygon hit exists anywhere in the visible draw:
+    return the closest polygon winner
+if any drawing-sphere hit exists:
+    return the closest sphere fallback
+return no object
+```
+
+Important consequences:
+
+- The broad phase is each visible **GfxObj part's drawing sphere**, not a Setup
+  selection sphere, physics collision shape, fixed creature hit box, or expanded
+  screen rectangle.
+- A polygon hit on any visible part beats every sphere-only fallback.
+- Retail does not ray-test world-cell walls as a second, independent occluder.
+  Occlusion is inherited from the same portal/viewcone draw traversal that decides
+  which parts may call `GfxObjUnderSelectionRay`.
+- `BSPTREE::GetSphere @ 0x005397E0` returns the drawing BSP root sphere exactly;
+  the DAT source is `GfxObj.DrawingBSP.Root.BoundingSphere`.
+
+## Vivid target indicator
+
+`VividTargetIndicator::SetSelected @ 0x004F5CE0`
+
+```text
+if selected id is the player: clear it
+if object is player-owned or IN_CONTAINER: clear it
+publish the remaining id to SmartBox
+if enabled and an id remains:
+    color = gmRadarUI::GetBlipColor(selected id)
+else:
+    hide both indicator roots
+```
+
+`VividTargetIndicator::Initialized @ 0x004F6C60`
+
+```text
+onscreenRoot = child 0x10000038
+corners = children 0x10000039, 0x1000003A, 0x1000003B, 0x1000003C
+offscreenRoot = child 0x10000045
+```
+
+The constructor resolves twelve source surfaces by calling `DBObj::GetByEnum`
+with RenderSurface DBO type `0x0C`, client-enum category `0x10000009`, and
+enum values `1..12`. Values `1..4` are the four on-screen corners.
+`CopyImage @ 0x004F5DD0`
+uses the active retail blit mode (`s_BlitMethod == 4`) to colorize the source
+art with the same color as the object's radar blip.
+
+`VividTargetIndicator::OnDraw @ 0x004F62B0` (on-screen branch)
+
+```text
+if disabled, no selected id, or selected part was not reported by this world draw:
+    hide indicator
+else:
+    colorize the four DAT corner images with the selected radar-blip color
+    obtain the selected object's SmartBox screen rectangle
+    use the actual DAT corner width and height
+    place the corner images just outside the rectangle
+    clamp the assembled indicator to an 8-pixel viewport margin
+    show the on-screen root and hide the off-screen root
+```
+
+There is no selected-world-mesh tint or luminosity mutation in
+`CPhysicsPart::Draw`, `ACCWeenieObject::SetSelected`, or the world mesh draw
+path. The visible notification is the colorized four-corner DAT indicator. A
+mesh shader tint would therefore be a new effect, not a retail port.