fix(editor): zone drafting respects the snapping mode + shows its HUD chip

Two zone fixes.

helper-manager: the contextual HUD only rendered for tools with `def.toolHints`,
so zone (none) showed no HUD and no snapping chip even though it resolves a snap
context. Render the generic RegisteredToolHelper whenever the tool has hints OR a
snap/continuation context; hoist the legacy `roof` RoofHelper above it so the new
fallback doesn't capture it. Any snappable hint-less draft tool now advertises
Shift = cycle.

zone-tool: a not-yet-migrated legacy tool — it used Shift as a snap bypass and
applied `gridSnapStep` unconditionally, so Off mode still snapped to grid.
Migrated to the mode-driven exclusive-modes convention (zone resolves to the
'wall' context): grid quantize gated on isGridSnapActive(), 15° ray gated on
isAngleSnapActive(), Off/Lines leave the raw cursor. Dropped the Shift-bypass and
its key listeners — Shift now cycles the mode globally. Recorded as migrated in
the review skill's known-legacy list.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.agents/skills/review-architecture/SKILL.md

@@ -148,7 +148,7 @@ Apply when the diff touches a tool, a `move-tool` / `selection` / endpoint / res
 - **Snappable kinds declare `snapProfile`.** A kind whose tool snaps but whose `NodeDefinition` omits `snapProfile` (`'item' | 'structural'`) gets no contextual chip and the wrong default mode-set — flag it (suggestion, blocker if it ships a bespoke per-kind snapping switch instead).
 - **Bespoke movers must not open a `moving` scope.** `useMovingNode()` reads the scope, and `tool-manager` mounts the generic `MoveRegistryNodeTool` whenever it's non-null. A bespoke `move-tool.tsx` that calls `begin(movingScope(...))` or `setMovingNode(node)` re-creates the dual-path double-handling (FPS collapse / teleport on move). **Blocker.** Mode-driven snapping inside a bespoke mover must resolve the mode without a global `moving` / `reshaping` scope (see `interaction-scope.md` § "Snapping mode & modifiers").
 - **`event.altKey` is not an alignment bypass.** A drafting/preview path that reads `event.altKey` to suppress Figma-alignment is a **blocker** in any **new** or **touched** tool — alignment follows the magnetic snap mode (`bypass: !isMagneticSnapActive()`). Alt is force/free for placement/move; it is **not** a snap/alignment modifier. The one sanctioned Alt use outside force is the **wall/fence chain-mode toggle** (clean Alt-tap → `cycleWallChainMode` / `cycleFenceChainMode`, via `hooks/use-keyboard.ts` `isChainModeContext()`), allowed only because wall/fence drafting has no force role. Grep tell: `event.altKey` near an `align` / `bypass` expression in a `tool.tsx` / floorplan preview path.
-- **Known-legacy exceptions (migrate on touch).** Tracked debt in `plans/editor-placement-interaction-overhaul.md`; a PR that **touches** one must migrate it, not extend it; a **new** tool on either legacy pattern is a blocker regardless. (1) `shiftKey` snap-bypass in the MEP move/endpoint tools (`packages/nodes/src/{duct-segment,pipe-segment,liquid-line,lineset,duct-fitting}/{move-tool,selection}.tsx`). (2) `altKey` alignment-bypass in the roof / polygon / slab pointer-move previews (`components/editor/floorplan-panel.tsx`) and the `resolveSlabPlanPointSnap` / `resolveCeilingPlanPointSnap` paths. **Already migrated — do not regress:** wall + fence drafting (both modifier patterns).
+- **Known-legacy exceptions (migrate on touch).** Tracked debt in `plans/editor-placement-interaction-overhaul.md`; a PR that **touches** one must migrate it, not extend it; a **new** tool on either legacy pattern is a blocker regardless. (1) `shiftKey` snap-bypass in the MEP move/endpoint tools (`packages/nodes/src/{duct-segment,pipe-segment,liquid-line,lineset,duct-fitting}/{move-tool,selection}.tsx`). (2) `altKey` alignment-bypass in the roof / polygon / slab pointer-move previews (`components/editor/floorplan-panel.tsx`) and the `resolveSlabPlanPointSnap` / `resolveCeilingPlanPointSnap` paths. **Already migrated — do not regress:** wall + fence drafting (both modifier patterns) and `zone` drafting (`components/tools/zone/zone-tool.tsx` — mode-driven grid/angle gates, no Shift bypass).
 
 ## 5. Output format