Selection: registry-driven, drop spawn flag, restore green color

Two concerns from the spike:

1) Selection / floating-action-menu had hardcoded kind lists scattered
   across 4 files. Adding 'shelf' to each one per migration was the
   wrong abstraction — the user's question "did you make it generic
   from the noderegistry?" was the right one. Done now.

   Added to @pascal-app/core/registry:
   - getSelectableKinds(): string[] — returns all registered kinds
     whose definition declares `capabilities.selectable`.
   - isRegistrySelectable(kind): boolean — predicate for OR-chains.

   Refactored hardcoded sites to merge registry kinds at runtime,
   keeping legacy hardcoded lists intact so existing kinds keep
   working unchanged:
   - editor SelectionManager: 4 subscription loops (enter/leave/click)
     + structure.isValid + getSelectionTarget — all augment with
     registry kinds. Phase 6 deletes the hardcoded lists.
   - viewer SelectionManager: subscription loop + SelectableNodeType
     broadened with `(string & {})` to accept registry kinds.
   - floating-action-menu: ALLOWED_TYPES OR'd with isRegistrySelectable.
   - Removed the manually-added 'shelf' entries from previous commit
     857ddd4; they were redundant once the registry-driven path landed.

   Future built-in nodes that declare `capabilities.selectable` get
   click-selection + hover + the floating action menu (move/delete
   icons) for free, no editing of these 4 files.

2) Spawn parity is signed off. Drop the
   NEXT_PUBLIC_USE_REGISTRY_FOR_SPAWN flag entirely; spawn registers
   unconditionally in builtinPlugin.nodes. Restored SPAWN_COLOR to
   the original #22c55e green (was #ef4444 red as a Phase 2
   verification marker).

Pre-existing typecheck errors in editor (ceiling/fence/slab tree-node,
scene.ts buildingId) are unchanged.

630 tests still pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/nodes/src/spawn/renderer.tsx

@@ -5,13 +5,7 @@ import { useNodeEvents, useViewer } from '@pascal-app/viewer'
 import { useMemo, useRef } from 'react'
 import { Color, type Group, Shape } from 'three'
 
-// TEMPORARY (Phase 2 verification): the registry-driven renderer paints
-// spawns RED so you can visually tell which dispatch path is live. The
-// legacy renderer in @pascal-app/viewer is still green. Revert this to
-// '#22c55e' once the registry path is signed off for parity. Tracked by
-// the NEXT_PUBLIC_USE_REGISTRY_FOR_SPAWN flag — if a spawn renders red
-// you're on the new path; green = legacy.
-const SPAWN_COLOR = new Color('#ef4444')
+const SPAWN_COLOR = new Color('#22c55e')
 
 /**
  * Registry-driven spawn renderer. Behaviorally identical to the legacy