fix(dataprotection): preserve backup namespace for cross-namespace restores

[leon-ape]

Backport of #10827 for release-1.1; related issue: #10829.

The final #10827 diff cannot be cherry-picked cleanly onto this branch: it conflicts in pkg/controller/plan/restore_test.go, and pkg/dataprotection/restore/utils_test.go is absent from the original release base. This PR applies the same behavior to the release-specific controller layout and keeps tests in the standard restore_test.go, utils_test.go, and manager_test.go files.

What changed

• Preserve the referenced Backup namespace in the release-specific preview, prepare-data, and post-ready Restore paths.
• Keep the existing default support for non-VolumeSnapshot cross-namespace Backup references; do not introduce ReferenceGrant or a new authorization contract.
• Keep the existing TODO for a future general cross-namespace permission check.
• Resolve the complete restore dependency chain before rejecting cross-namespace VolumeSnapshot Backups, including PITR-selected base snapshots.
• Preserve the VolumeSnapshot marker on continuous restore base Backup sets.
• Reject a PITR-selected base Backup without status.backupMethod with a fatal error instead of panicking while reading snapshotVolumes.
• Explicitly document cross-namespace VolumeSnapshot restore as NOT supported and regenerate CRDs and API reference docs.
• Keep the focused tests aligned with fix(dataprotection): preserve backup namespace for cross-namespace restores #10827 and place them in the standard test files.
• Synchronize the branch with the latest release-1.1, retaining both sides of the utils_test.go additions.

Validation

• scripts/codex-go-test.sh ./pkg/dataprotection/restore ./pkg/controller/plan ./controllers/dataprotection ./pkg/operations -count=1
• make manifests
• make doc
• git diff --check

All targeted tests pass.

[apecloud-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.70%. Comparing base (619a34a) to head (c3118cf).

Files with missing lines	Patch %	Lines
pkg/dataprotection/restore/utils.go	70.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           release-1.1   #10833   +/-   ##
============================================
  Coverage        55.69%   55.70%           
============================================
  Files              550      550           
  Lines            62421    62434   +13     
============================================
+ Hits             34767    34777   +10     
- Misses           24334    24345   +11     
+ Partials          3320     3312    -8     

Flag	Coverage Δ
unittests	55.70% <87.50%> (+<0.01%)	⬆️

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[leon-ape]

/approve