Sprint: Idee regril mogelijkheid (#144)

* feat(ST-cmovhveef): add PLANNED to GRILL_TRIGGERABLE_FROM and PLANNED→GRILLING transition

- GRILL_TRIGGERABLE_FROM now includes 'PLANNED' in actions/ideas.ts
- ALLOWED_TRANSITIONS PLANNED entry extended with 'GRILLING' in lib/idea-status.ts
- Updated canTransition test to reflect the new re-grill-from-PLANNED behavior

* test(ST-cmovhvef3): add exhaustive re-grill canTransition test covering PLANNED

Adds a loop test that asserts canTransition(status, 'GRILLING') for all
statuses in GRILL_TRIGGERABLE_FROM that support the transition, explicitly
documenting PLANNED as a valid re-grill entry point.

* feat(ST-cmovhvegf): add existingPbi pre-check in materializeIdeaPlanAction

- Adds options.allowAlongside parameter to control behaviour when a PBI
  with executed tasks already exists.
- Returns 409 PBI_HAS_ACTIVE_TASKS:<code> when tasks are DONE/IN_PROGRESS
  and allowAlongside is not set.
- Auto-deletes the old PBI inside the transaction when no tasks have been
  executed (atomic replace).
- Alongside mode (allowAlongside=true) skips deletion and creates a new PBI.

* test(ST-cmovhveh3): add pre-check integration tests for materializeIdeaPlanAction

Three new scenarios in ideas-crud.test.ts:
- auto-vervang: old PBI deleted in transaction when no executed tasks
- conflict-409: returns PBI_HAS_ACTIVE_TASKS:<code> with active tasks
- alongside: skips delete and creates new PBI when allowAlongside=true
Also adds task.count, pbi.findUnique, pbi.delete to prisma mock.

* feat(ST-cmovhveih): remove PLANNED-blokkering in idea-row-actions, add inline Bekijk-PBI button

- Removed grillBlockedReason guard for status==='planned', enabling re-grill from PLANNED
- Removed the early return for PLANNED that hid all standard buttons
- Added conditional 'Bekijk <code>' button at the start of the standard button set,
  visible only when status==='planned' and PBI + product_id are present

* feat(ST-cmovhvej7): add PBI_HAS_ACTIVE_TASKS alongside-dialoog in materialize handler

When materializeIdeaPlanAction returns code 409 with PBI_HAS_ACTIVE_TASKS:<code>,
a confirm dialog offers the user a choice: create new PBI alongside the existing one
or cancel. Alongside=true retries the action; cancel leaves the idea in PLAN_READY.

components/ideas/idea-row-actions.tsx

@@ -61,7 +61,6 @@ export function IdeaRowActions({ idea, isDemo, onArchive }: IdeaRowActionsProps)
   // ---- Grill Me ----
   const grillBlockedReason = (() => {
     if (status === 'grilling' || status === 'planning') return 'Job loopt al'
-    if (status === 'planned') return 'Idee is gepland — open de PBI'
     if (!hasProductWithRepo) return 'Idee heeft een product met repo nodig'
     if (!workerOk) return 'Geen Claude-worker actief'
     return null
@@ -108,15 +107,24 @@ export function IdeaRowActions({ idea, isDemo, onArchive }: IdeaRowActionsProps)
   function handleMaterialize() {
     if (!confirm('Plan materialiseren? Dit maakt PBI + stories + taken aan.')) return
     startTransition(async () => {
-      const r = await materializeIdeaPlanAction(idea.id)
+      let r = await materializeIdeaPlanAction(idea.id)
+
+      if ('error' in r && r.code === 409 && r.error.startsWith('PBI_HAS_ACTIVE_TASKS:')) {
+        const pbiCode = r.error.split(':')[1]
+        const alongside = confirm(
+          `De bestaande PBI (${pbiCode}) heeft uitgevoerde taken.\n` +
+          `OK = nieuwe PBI naast bestaande aanmaken.\n` +
+          `Annuleren = stoppen.`
+        )
+        if (!alongside) return
+        r = await materializeIdeaPlanAction(idea.id, { allowAlongside: true })
+      }
+
       if ('error' in r) {
         toast.error(r.error)
         return
       }
       toast.success(`Gematerialiseerd als ${r.data?.pbi_code}`)
-      // Navigeer naar de product-backlog. Anchor-scrolling per-PBI bestaat
-      // (nog) niet in pbi-list, dus gewoon naar de overview-pagina; de nieuwe
-      // PBI is de meest recente.
       if (idea.product_id) {
         router.push(`/products/${idea.product_id}`)
       } else {
@@ -125,35 +133,20 @@ export function IdeaRowActions({ idea, isDemo, onArchive }: IdeaRowActionsProps)
     })
   }
 
-  // PLANNED-state: kortere variant met "Bekijk PBI"-link
-  if (status === 'planned' && idea.pbi && idea.product_id) {
-    return (
-      <div className="flex items-center gap-1.5">
+  return (
+    <div className="flex items-center gap-1">
+      {/* Bekijk PBI — alleen zichtbaar in PLANNED */}
+      {status === 'planned' && idea.pbi && idea.product_id && (
         <Button
-          size="sm"
           variant="outline"
-          onClick={() =>
-            router.push(`/products/${idea.product_id}`)
-          }
+          size="sm"
+          onClick={() => router.push(`/products/${idea.product_id!}`)}
         >
           Bekijk {idea.pbi.code}
           <ExternalLink className="ml-1 size-3.5" />
         </Button>
-        <Button
-          size="sm"
-          variant="ghost"
-          onClick={() => router.push(`/ideas/${idea.id}`)}
-          aria-label="Open idee"
-          title="Open idee"
-        >
-          <ArrowRight className="size-4" />
-        </Button>
-      </div>
-    )
-  }
+      )}
 
-  return (
-    <div className="flex items-center gap-1">
       {/* Grill Me */}
       <ActionButton
         label="Grill"