docs(testing): add PlanAction JWT hydration implementation guide

Add comprehensive implementation guide for creating PlanAction claims
via hydratePlan() function pattern, following established hydrateGive()
and hydrateOffer() patterns.

Changes:
- Add hydrate-plan-implementation-guide.md with complete implementation
  details, usage examples, and testing recommendations
- Link implementation guide from getting-valid-plan-ids.md Method 6
- Link implementation guide from localhost-testing-guide.md Option B

The guide provides:
- Complete hydratePlan() function implementation
- PlanActionClaim interface structure
- Helper functions (createAndSubmitPlan, editAndSubmitPlan)
- Usage examples and edge cases
- Testing recommendations and security considerations

This complements plan creation documentation by showing how to
programmatically construct valid PlanAction JWTs for POST /api/v2/claim.

docs/getting-valid-plan-ids.md

@@ -78,6 +78,12 @@ Plans are created by importing JWT claims containing a `PlanAction`:
 - JWT must be signed with a valid DID key
 - Response includes `handleId` and `planId` if creation succeeds
 
+**Implementation Guide**: See [`docs/hydrate-plan-implementation-guide.md`](./hydrate-plan-implementation-guide.md) for complete implementation details, including:
+- `hydratePlan()` function pattern
+- PlanActionClaim interface structure
+- Helper functions for create/edit operations
+- Usage examples and testing recommendations
+
 **Note**: This method requires generating signed JWTs with DID keys, which is complex. **Method 1 (TimeSafari App UI) is recommended** for creating test plans.
 
 ## Plan Handle ID Format