chat: improve ChatApprovedAccountOrganizations restriction messaging

[joshspicer]

Reframes the ChatApprovedAccountOrganizations gate messaging to clearly attribute the restriction to the administrator, rather than using passive "approved organization" language that could imply VS Code itself controls the list.

Changes

Notifications (accountPolicyGateContribution.ts):

• New shape: "Your administrator restricts AI features to GitHub accounts in the following organizations: {orgs}. The account "{name}" is not a member of any of these."
• Unified the previously split OrgNotApproved vs noAccount/wrongProvider branches into a single consistent message shape
• Removed "Contact your administrator for more information." and "Sign into an approved GitHub account" — the org list and Sign In button are self-explanatory
• Wildcard (*) case: "Your administrator restricts AI features to specific GitHub accounts. The account "{name}" does not qualify."

Splash screen (sessionsPolicyBlocked.ts):

• Title: "Sign-In Required by Your Administrator" (was "Sign-In Required")
• Body (with account): "The account "{name}" is not a member of an organization that your administrator allows for Agents."
• Body (no account): "Your administrator restricts Agents to members of the organizations below."
• Org list heading: "Allowed organizations:" (was "Approved organizations:")
• Footer: dropped "Contact your administrator for more information." — the title already names the source

Refs #312534

[github-actions]

No screenshot changes.

[Copilot]

Pull request overview

This PR updates user-facing messaging for the ChatApprovedAccountOrganizations policy gate to clearly attribute restrictions to the user’s administrator (instead of implying VS Code controls “approved orgs”), both in VS Code notifications and the Agents app blocked overlay.

Changes:

• Rewords policy-gate notifications to use consistent “administrator restricts …” language and simplifies branching.
• Updates the Agents app policy-blocked splash screen title/body/org heading to match the new framing and removes the “contact your administrator” footer text.
• Adjusts wildcard (*) messaging to a “specific GitHub accounts” framing.

Show a summary per file

File	Description
src/vs/workbench/services/policies/browser/accountPolicyGateContribution.ts	Reframes and unifies notification text for the account policy gate, including org list and wildcard cases.
src/vs/sessions/contrib/policyBlocked/browser/sessionsPolicyBlocked.ts	Rewords Agents “policy blocked” overlay copy (title/body/heading/aria-label) and removes the footer contact text.

Copilot's findings

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

[joshspicer]

@copilot

• keep the header title 'Sign-in Required' (so it's one line still).
• keep the 'contact your administrator for more information'

[Copilot]

@copilot

• keep the header title 'Sign-in Required' (so it's one line still).
• keep the 'contact your administrator for more information'

Addressed in 85f9e63: the Agents blocked overlay title is back to "Sign-In Required" and the administrator contact guidance is restored.

Screenshot: https://github.com/user-attachments/assets/f4161210-3578-4629-820e-85c0f36fcfd1