fix(dataprotection): redirect postReady for multi-component restores

[weicao]

Fixes #10418.

Summary

• supersedes the controller-code portion of fix(dp): postReady-only redirect for multi-component logical backup restore #10423 with a clean controller-owned branch
• redirects non-matching restore PVC postReady handling to the backup target component instead of silently completing it
• keeps sharding missing-target skipPostReady as skip-only instead of treating every skip as redirectable
• keeps the cluster-wide PVC bound wait and target-component NotFound requeue behavior from fix(dp): postReady-only redirect for multi-component logical backup restore #10423
• fills redirected Restore ReadyConfig from the effective backup target so Strategy, required policy, and target volume mounts match the normal source-target path
• adds regressions for the TiDB PITR prepareData+postReady shape, sharding skip-only behavior, and redirected postReady execution fields

Validation

• PASS: go generate ./pkg/testutil/k8s/mocks (local compile prerequisite)
• PASS: go test ./controllers/dataprotection -run 'TestEnsurePostReadyRestore_(ShardingMissingTargetSkip_DoesNotRedirect|MultiComponent_(PrepareDataAndPostReady_RedirectsPostReady|PostReadyOnly_ShouldNotSilentlySkip|PostReadyOnly_TargetComponentNotYetCreated|PostReadyOnly_WaitsForAllComponentPVCs|PostReadyOnly_TargetsSlice|PostReadyRedirectPreservesTargetExecutionFields))|TestDecidePVCRestore_MultiComponent_PostReadyOnly_SkipsNonMatchingPVC|TestDecidePVCRestoreAssignsShardingTargetsByStableComponentOrder|TestRebindPVCAndPV_NilPopulatePVC_ReturnsFatalError' -count=1
• PASS: git diff --check -- controllers/dataprotection/volumepopulator_controller.go controllers/dataprotection/volumepopulator_controller_test.go
• BLOCKED locally: go test ./controllers/dataprotection -count=1 cannot start envtest because /usr/local/kubebuilder/bin/etcd is absent; 0 envtest specs ran

Evidence boundary

TiDB PITR on PR1/idc4 reported 13P/1F/0S, with PITR.6 showing zero postReady Restore CRs on #10423 head 95b0723. This PR fixes the controller path and closes the local regression gate. A TiDB PITR runtime rerun against this PR head is still required for addon acceptance.

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[codecov]

Codecov Report

❌ Patch coverage is 60.43165% with 55 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.16%. Comparing base (d8cbb03) to head (082f164).

Files with missing lines	Patch %	Lines
...llers/dataprotection/volumepopulator_controller.go	60.43%	38 Missing and 17 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10466      +/-   ##
==========================================
+ Coverage   62.10%   62.16%   +0.05%     
==========================================
  Files         533      533              
  Lines       63722    63839     +117     
==========================================
+ Hits        39577    39687     +110     
+ Misses      20547    20546       -1     
- Partials     3598     3606       +8     

Flag	Coverage Δ
unittests	62.16% <60.43%> (+0.05%)	⬆️

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[weicao]

Updated in 082f164. Sharding PVCs now resolve through the sharding order before the single-target selector fallback, and postReady redirect re-checks the sharding source-target result so missing-target shards stay skip-only instead of redirecting to the unique backup target. Added TestEnsurePostReadyRestore_ShardingSingleTargetMissingTargetSkip_DoesNotRedirect. Focused suite and TestDecidePVCRestore passed locally; CI is rerunning.