fix(mcp): restore >0 validation and reject ambiguous numbers in measurement()

Adversarial-review follow-ups to the lingo measurement() field:
- Add a `positive` option (strict > 0) and use it for the non-zero dimension
  params. Swapping z.number().positive() → measurement(..,{min:0}) had started
  admitting 0 (the core node schemas have no positivity backstop), so a zero-size
  wall/opening/roof could be created. Inclusive-0 fields (overhang, sill height,
  knee-wall height, opening offset, roof pitch) keep min:0.
- Escalate AMBIGUOUS_NUMBER to error so "1,234" fails instead of silently reading
  as 1234 — a 1000x hazard for European decimals. Matches lingo's own /ai fields.
- roofLevelElevation reverted to z.number() (it's a level ordinal, not meters);
  radians fields now advertise radian-appropriate examples.

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

packages/mcp/src/tools/create-wall.ts

@@ -12,8 +12,11 @@ export const createWallInput = {
   levelId: NodeIdSchema,
   start: Vec2Schema,
   end: Vec2Schema,
-  thickness: measurement('length', 'm', { min: 0, description: 'Wall thickness.' }).optional(),
-  height: measurement('length', 'm', { min: 0, description: 'Wall height.' }).optional(),
+  thickness: measurement('length', 'm', {
+    positive: true,
+    description: 'Wall thickness.',
+  }).optional(),
+  height: measurement('length', 'm', { positive: true, description: 'Wall height.' }).optional(),
 }
 
 export const createWallOutput = {