sessions: include AGENTS.md in instructions listing

[joshspicer]

The sessions AI customization tree view and overview were only calling listPromptFiles(PromptsType.instructions) to discover instruction files. However, AGENTS.md (along with CLAUDE.md and copilot-instructions.md) is classified as an agent type by getPromptFileType(), so it was never returned by that call — making these files invisible in the Instructions section.

Fix

Call listAgentInstructions() alongside listPromptFiles() and merge the results (deduplicating by URI). This matches the pattern already used by the workbench customization editor in aiCustomizationListWidget.ts.

Changed files

• aiCustomizationTreeViewViews.ts — getStorageGroups() now merges agent instruction files into the instructions list
• aiCustomizationOverviewView.ts — loadCounts() now includes agent instruction files in the instructions count badge

[Copilot]

Pull request overview

Updates the Sessions window AI customization sidebar views so that agent instruction files (e.g. AGENTS.md, CLAUDE.md, copilot-instructions.md) are included in the “Instructions” discovery paths, matching the workbench customization editor behavior.

Changes:

• Merge listAgentInstructions() results into the “Instructions” listing in the sessions customization tree view (with URI de-duping).
• Include agent instruction files in the “Instructions” count shown in the sessions customization overview.

Show a summary per file

File	Description
src/vs/sessions/contrib/aiCustomizationTreeView/browser/aiCustomizationTreeViewViews.ts	Adds agent instruction files into the instructions list used for grouping/rendering in the tree view.
src/vs/sessions/contrib/aiCustomizationTreeView/browser/aiCustomizationOverviewView.ts	Adds agent instruction files into the instructions count calculation (with URI de-duping).

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[Copilot]

Agent instruction files returned from listAgentInstructions() can come from user-level locations (e.g. ~/.claude/CLAUDE.md). This code always injects them as storage: PromptsStorage.local, which will mis-group them under “Workspace”, skew the group counts, and set the wrong itemStorage context key for menus. In src/vs/sessions/contrib/sessions/browser/customizationCounts.ts the storage is derived based on whether the URI is inside a workspace folder/active root; this view should apply the same classification (or extend listAgentInstructions() to return storage) before pushing items into allItems.

Suggested change

	allItems.push({ uri: file.uri, storage: PromptsStorage.local, type: PromptsType.instructions });
	const storage = this.workspaceContextService.getWorkspaceFolder(file.uri) ? PromptsStorage.local : PromptsStorage.user;
	allItems.push({ uri: file.uri, storage, type: PromptsType.instructions });