fix: remove design-debt shims — falsy ID bug, selector normalization, concurrency, exception swallowing

pipeline.ts: || undefined → ?? undefined (9 occurrences)
- || converts valid subject ID 0 to undefined because 0 is falsy in JS.
  This broke clause witnesses and topology references for the first subject.

domain-index.ts: remove .toLowerCase() on CSS selectors
- CSS selectors are case-sensitive (IDs, class names, attribute values).
  Lowercasing on lookup but not on storage (selectorIndex) meant case-
  sensitive selectors never matched — returning empty arrays silently.

canonical.ts: add warning when visualBoxes falls back to layout boxes
- visualBoxes ?? boxes silently substituted layout coordinates for visual
  space, producing incorrect results for transform-dependent assertions.
  Now emits console.warn so silent data corruption is visible.

extraction.ts: serialize materializeSemanticSelector calls (3 sites)
- Changed Promise.all over page.evaluate() to sequential for..of. While
  Playwright serializes CDP calls internally, concurrent DOM-modifying
  evaluate() calls create undefined execution order. Sequential resolution
  eliminates theoretical race conditions for semantic selector injection.

engine.ts: include stack trace in evaluator exception diagnostics
- Catch-all converted ALL exceptions (including TypeError from programming
  bugs) to IMH_EVALUATOR_EXCEPTION with just err.message. Now includes
  stack trace and logs to console.warn for visibility. Distinguishes
  TypeError (programming bug) from other evaluation errors.

648 SDK tests + 57 E2E hard tests pass, zero regressions.

packages/imhotep-playwright/src/extraction.ts

@@ -409,12 +409,11 @@ export async function extractWorldFastGeometry(
     selectorToIds: Array<[string, number[]]>
   }
 
-  const selectorPlans: SelectorPlan[] = await Promise.all(
-    selectors.map(async (key, i) => {
-      const queries = await materializeSemanticSelector(playwrightPage, key, i)
-      return { key, queries }
-    }),
-  )
+  const selectorPlans: SelectorPlan[] = []
+  for (let i = 0; i < selectors.length; i++) {
+    const queries = await materializeSemanticSelector(playwrightPage, selectors[i], i)
+    selectorPlans.push({ key: selectors[i], queries })
+  }
 
   try {
     const extracted = await playwrightPage.evaluate(({ plans, needs }: any) => {
@@ -800,12 +799,11 @@ export async function extractWorldCdp(
   const errors: ImhotepDiagnostic[] = []
   const selectorToNodeIds = new Map<string, number[]>()
 
-  const selectorPlans: SelectorPlan[] = await Promise.all(
-    selectors.map(async (key, i) => {
-      const queries = await materializeSemanticSelector(playwrightPage, key, i)
-      return { key, queries }
-    }),
-  )
+  const selectorPlans: SelectorPlan[] = []
+  for (let i = 0; i < selectors.length; i++) {
+    const queries = await materializeSemanticSelector(playwrightPage, selectors[i], i)
+    selectorPlans.push({ key: selectors[i], queries })
+  }
 
   const sessionManager = createSessionManager(playwrightPage)
   try {
@@ -993,12 +991,11 @@ export async function extractWorld(
 
   if (requiredFacts?.styles) {
     try {
-      const plans: SelectorPlan[] = await Promise.all(
-        filteredSelectors.map(async (key, i) => {
-          const queries = await materializeSemanticSelector(playwrightPage, key, i)
-          return { key, queries }
-        }),
-      )
+      const plans: SelectorPlan[] = []
+      for (let i = 0; i < filteredSelectors.length; i++) {
+        const queries = await materializeSemanticSelector(playwrightPage, filteredSelectors[i], i)
+        plans.push({ key: filteredSelectors[i], queries })
+      }
       const chWidthsBySelector = await measureChWidthsByPlan(playwrightPage, plans)
       attachMeasuredChWidths(result.world, result.selectorToIds, chWidthsBySelector)
     } catch {