[access-dev-tunnel-cutover] - Remove GitHub Entra and anonymous token providers

[JoshuaRowePhantom]

Part of #1513 and master #1505

Parent

• Direct parent: [access-dev-tunnel] - Track identity Connect-token and bounded-renewal slices #1513.
• Architecture master: [access-broker] - Unify credential-use authorization, acquisition, renewal, and presentation #1505.

Dependencies

• Depends on: [access-dev-tunnel-identity] - Implement typed Dev Tunnel identity routes #1557.

Summary

Delete the three simple legacy identity-provider implementations after typed route execution lands.

Current Limitation / Root Cause

GitHubDevTunnelAuthTokenProvider, EntraDevTunnelAuthProvider, and AnonymousDevTunnelAuthProvider still implement the removed parallel provider interface.

Affected Files

Path	Change
Phantom.Workspaces/Services/DevTunnel/GitHubDevTunnelAuthTokenProvider.cs	Remove or update only the named bounded production surface.
Phantom.Workspaces/Services/DevTunnel/EntraDevTunnelAuthProvider.cs	Remove or update only the named bounded production surface.
Phantom.Workspaces/Services/DevTunnel/AnonymousDevTunnelAuthProvider.cs	Remove or update only the named bounded production surface.
Focused test file	Add only the tests listed below.

Design / Fix

// Remove GitHubDevTunnelAuthTokenProvider.
// Remove EntraDevTunnelAuthProvider.
// Remove AnonymousDevTunnelAuthProvider.

DevTunnelIdentityCredentialAccessExecutor is the only remaining identity route implementation.

Security and Privacy Invariants

• No credential material, provider artifact, unsafe identifier, or raw provider output is introduced or copied during removal.
• Replacement callers already use typed broker requests and caller-owned leases.
• Removal fails the build if an undeclared production reference remains; it does not leave a fallback.

Exclusions

• No unrelated provider, UI, persistence-format, or behavioral redesign.
• No bridge, migration reader, or dual production path.

Commit Plan

Commit 1 — [access-dev-tunnel-cutover] - Remove GitHub Entra and anonymous token providers

Production types: GitHubDevTunnelAuthTokenProvider, EntraDevTunnelAuthProvider, AnonymousDevTunnelAuthProvider.

Acceptance: one independently buildable commit affecting only the files above plus AccessMigrationTests.

Expected Tests

Test Name	Class	What It Verifies
AccessMigration_DevTunnelTree_HasNoGitHubTokenProvider	AccessMigrationTests	Verifies the bounded cutover with no remaining production reference.
AccessMigration_DevTunnelTree_HasNoEntraTokenProvider	AccessMigrationTests	Verifies the bounded cutover with no remaining production reference.
AccessMigration_DevTunnelTree_HasNoAnonymousTokenProvider	AccessMigrationTests	Verifies the bounded cutover with no remaining production reference.