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

[leon-ape]

Backport of #10827 for release-1.0; 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-1.0, 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]

Auto Cherry-pick Instructions

Usage:
  - /nopick: Not auto cherry-pick when PR merged.
  - /pick: release-x.x [release-x.x]: Auto cherry-pick to the specified branch when PR merged.

Example:
  - /nopick
  - /pick release-1.1

CLA Recheck Instructions

Usage:
  - /recheck-cla: Trigger a re-check of CLA status for this pull request.
Example:
  - /recheck-cla

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.31%. Comparing base (1d97fb1) to head (580d55b).
⚠️ Report is 1 commits behind head on release-1.0.

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-1.0   #10834      +/-   ##
===============================================
+ Coverage        54.14%   54.31%   +0.16%     
===============================================
  Files              495      495              
  Lines            55950    56066     +116     
===============================================
+ Hits             30296    30450     +154     
+ Misses           22647    22589      -58     
- Partials          3007     3027      +20     

Flag	Coverage Δ
unittests	54.31% <87.50%> (+0.16%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[leon-ape]

/approve