Make remote comparison ignore casing

[dkurepa]

#6268

[Copilot]

Pull request overview

This PR improves reliability of PCS/Darc codeflow operations by making conflict resolution logic more robust (including added/deleted-file conflicts) and by handling Git remote URL casing mismatches that can block subscriptions (Issue #6268).

Changes:

• Make target-repo remote lookup case-insensitive when updating remotes for manual-conflict-resolution PRs.
• Refactor crossing-flow patch creation logic into a shared helper and add a dedicated path for reapplying crossing-flow changes to non-conflicted files.
• Enhance LocalGitClient.ResolveConflict to correctly resolve non-“both modified” conflict shapes (e.g., add/delete) using git status --porcelain.

Reviewed changes

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

File	Description
src/ProductConstructionService/ProductConstructionService.DependencyFlow/PullRequestUpdaters/CodeFlowPullRequestUpdater.cs	Fixes remote matching when subscription URL casing differs from git remote -v.
src/Microsoft.DotNet.Darc/DarcLib/VirtualMonoRepo/ForwardFlowConflictResolver.cs	Adds logic to auto-resolve conflicts outside the flowed repo path (but see blocking comment).
src/Microsoft.DotNet.Darc/DarcLib/VirtualMonoRepo/CodeFlowConflictResolver.cs	Extracts crossing-flow patch creation and adds reapply logic for partial-revert repair scenarios.
src/Microsoft.DotNet.Darc/DarcLib/LocalGitClient.cs	Improves conflict resolution to handle add/delete variants and avoid invalid checkout --ours/--theirs calls.