chat: Make customizations multi-root workspace aware

[Jessie Houghton (houghj16)]

Summary

• split workspace-backed customization sections by folder when two or more workspace folders are active
• keep the existing single-folder and empty-workspace presentation unchanged
• scope manual and AI-assisted customization creation to the workspace folder where the section action was invoked
• scope hook discovery, existing hook files, and hook destinations to the selected workspace folder
• reuse the source-line and MCP behavior already available on main instead of duplicating it

Customization pages

Agents, Skills, Instructions, Hooks, and Prompts

In a multi-root workspace, each folder now has its own named section instead of contributing to one combined Workspace section. Items are assigned using their containing workspace folder.

Section-level creation actions carry that folder through manual creation, root-file creation, hook configuration, and Generate with AI. Location pickers only offer destinations belonging to the selected folder.

In an empty or single-folder workspace, these pages continue to use the existing Workspace section and unscoped creation flow.

Plugins

The workspace-scoped Plugins section is split into named workspace-folder sections in multi-root workspaces. User, Remote Session, and Available sections are unchanged.

MCP Servers and row source labels

This PR does not change MCP row presentation or customization-row source labels. It uses the implementations that have since landed on main.

Testing

• npm run compile-client — passed
• scripts\test.bat src\vs\workbench\contrib\chat\test\browser\aiCustomization\aiCustomizationListWidget.test.ts src\vs\workbench\contrib\chat\test\browser\aiCustomization\customizationCreatorService.test.ts src\vs\workbench\contrib\chat\test\browser\aiCustomization\pluginListWidget.test.ts src\vs\workbench\contrib\chat\test\browser\promptSyntax\hookActions.test.ts — 66 passing
• targeted ESLint over all 14 changed TypeScript files — passed
• npm run valid-layers-check — passed
• git diff --check — passed

Fixes #332290
Fixes #333755
Addresses #332543

[Copilot]

Copilot review overview

🟡 Changes recommended

AI generation remains unscoped, and source/description information has accessibility and remote-workspace regressions.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Balanced
Findings: 3

New issues introduced by this change (3)

Severity	Finding
	src/​vs/​workbench/​contrib/​chat/​browser/​aiCustomization/​aiCustomizationItemSource.ts — Preserve source paths for remote workspace files
	src/​vs/​workbench/​contrib/​chat/​browser/​aiCustomization/​aiCustomizationListWidget.ts — Propagate the originating folder to AI generation
	src/​vs/​workbench/​contrib/​chat/​browser/​aiCustomization/​mcpListWidget.ts — Expose MCP provenance in the row's ARIA label

What changed in this PR

Makes AI customizations multi-root aware by grouping items per workspace folder and scoping manual creation flows.

Changes:

• Adds per-folder customization sections and source paths.
• Scopes manual customization and hook creation.
• Adds MCP provenance and updated tests/fixtures.

File	Description
aiCustomizationManagementEditor.fixture.ts	Adds MCP source fixtures.
hookActions.test.ts	Tests workspace hook filtering.
mcpListWidget.test.ts	Tests provenance and hover text.
customizationCreatorService.test.ts	Tests folder-scoped creation locations.
aiCustomizationListWidget.test.ts	Tests grouping, paths, and creation context.
hookActions.ts	Scopes hook selection and creation.
mcpListWidget.ts	Displays MCP source provenance.
customizationCreatorService.ts	Filters and labels creation destinations.
aiCustomizationManagementEditor.ts	Propagates workspace-folder context.
aiCustomizationListWidgetUtils.ts	Uses filenames as secondary text.
aiCustomizationListWidget.ts	Adds per-folder grouping and actions.
aiCustomizationItemSource.ts	Removes workspace prefixes from labels.

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