Fix remote agent change editor labels

[roblourens]

Fixes remote Agent Host changed-file editor titles leaking packed backing URIs.

This updates the Agents Changes view to derive editor labels/descriptions from the user-facing change URI while preserving the actual content resources used for deletion, diff, and file opens.

Validation:

• npm run compile-check-ts-native
• npm run gulp compile
• ./scripts/test.sh --run src/vs/sessions/contrib/changes/test/browser/changesEditorLabels.test.ts --run src/vs/workbench/services/label/test/browser/label.test.ts --grep "ChangesEditorLabels|agent host formatter labels wrapped remote file URIs"
• npm run valid-layers-check
• npm run precommit
• Live Agents window verification with Playwright/CDP and dap-cli

[Copilot]

Pull request overview

This PR addresses Agents Changes editor labels so remote agent-host resources display user-facing file paths instead of packed backing URIs.

Changes:

• Adds a shared getChangesEditorLabels helper for label/description derivation.
• Applies label overrides when opening single-file or diff editors from the Changes view.
• Adds coverage for agent-host URI label formatting and Changes editor label derivation.

Show a summary per file

File	Description
src/vs/sessions/contrib/changes/browser/changesEditorLabels.ts	Adds helper to derive editor label and description from a display URI.
src/vs/sessions/contrib/changes/browser/changesView.ts	Uses derived labels when opening deletion, diff, and modified-file editors.
src/vs/sessions/contrib/changes/test/browser/changesEditorLabels.test.ts	Tests display URI labels versus backing URI labels.
src/vs/workbench/services/label/test/browser/label.test.ts	Adds agent-host formatter coverage for wrapped remote file URIs.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 1