Remove self-signed TLS option (system trust only); add session changelog

Parity with the Android client: drop the "Allow self-signed certificate"
escape hatch. The app now performs system TLS trust only — a self-signed
appliance must have its CA installed on the device (MDM/profile). A code-only
public-key pinning policy remains (no UI).

- ServerTrustEvaluator: remove ServerTrustPolicy.allowSelfSignedForHost and its
  challenge handler; keep .system (default) and .pinPublicKeySHA256.
- SettingsView: remove the self-signed toggle/state/prefill; makeConfig uses
  the default .system policy.
- MCMSConnection / APIConfiguration: update usage-sketch + doc comments.
- README / GUI-NOTES / MCMS_API.md: document system-trust-only; self-signed
  boxes need their CA installed on the device.
- Add CHANGELOG.md for this session, flagged for the Android port.

Note: configs previously persisted with the self-signed policy fail to decode
and reset to defaults (one-time re-entry of the server URL).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

MCMSConnection.swift

@@ -37,18 +37,14 @@ final class MCMSConnection {
 /*
  USAGE SKETCH (delete once real views exist)
 
- // Direct access to the appliance with a self-signed cert on a controlled net:
- let url = URL(string: "https://10.2.10.29/api")!
+ // The appliance must present a CA-trusted cert (real cert, or an internal CA
+ // installed on the device via MDM/profile) — system trust only, no self-signed bypass:
+ let url = URL(string: "https://mcms.example.com/api")!
  let config = APIConfiguration(
      baseURL: url,
      apiVersion: "v1",                       // confirm /api/v1 vs /v1 from openapi.json
-     databaseId: nil,                        // or a specific DB id
-     trustPolicy: .allowSelfSignedForHost("10.2.10.29")
- )
-
- // Behind a reverse proxy with a real cert — change ONLY the URL + trust:
- // let config = APIConfiguration(baseURL: URL(string: "https://mcms.example.com")!,
- //                               trustPolicy: .system)
+     databaseId: nil                         // or a specific DB id
+ )                                            // trustPolicy defaults to .system
 
  let connection = MCMSConnection(config: config)