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.

lib/idea-status.ts

@@ -54,7 +54,7 @@ const ALLOWED_TRANSITIONS: Record<IdeaStatus, ReadonlyArray<IdeaStatus>> = {
   PLANNING: ['PLAN_READY', 'PLAN_FAILED'],
   PLAN_FAILED: ['PLANNING', 'GRILLED'],
   PLAN_READY: ['PLANNING', 'PLANNED'],
-  PLANNED: ['PLAN_READY'], // alleen via relinkIdeaPlanAction (PBI deleted)
+  PLANNED: ['PLAN_READY', 'GRILLING'], // PLAN_READY via relinkIdeaPlanAction; GRILLING via startGrillJobAction
 }
 
 export function canTransition(from: IdeaStatus, to: IdeaStatus): boolean {