Rename Web Analytics configuration

[thebuilder]

Summary

• rename the package configuration section from VercelAnalytics to WebAnalytics
• move the shared Vercel token to WebAnalytics__Providers__Vercel__AccessToken
• rename connection-specific token overrides to WebAnalytics__ConnectionAccessTokens__{guid}
• update the backoffice guidance, example configuration, README, and regression tests

Why

The package identity is Web Analytics and its configuration should support provider-specific settings without retaining the old Vercel-named root section. This is intentionally a breaking configuration change; no backward-compatibility aliases or fallbacks are included.

Impact

Existing installations must rename their configuration keys when upgrading. A release note should call out the breaking change.

Verification

• .NET test project passes
• focused settings dashboard tests pass (9 tests)
• TypeScript check passes
• git diff --check passes
• repository search confirms no legacy configuration keys remain

The full frontend run reached 137 passing tests; one unrelated OpenAPI generator test could not bind to 127.0.0.1 in the sandbox.