Retire the personality feature flag and document deprecated settings (#45809)

## What changed

- Accept and ignore `features.personality` in user configuration, profiles, and managed requirements.
- Remove feature gating from `personality = "none"`, which strips the literal `# Personality` section when preparing model catalog instructions. Preserve explicit base instructions and existing thread instructions.
- Document deprecated personality fields in configuration, app-server schemas, and the Python SDK: `friendly` and `pragmatic` no longer select a style, and `supportsPersonality` is always `false`.

## Testing

Add regression coverage for ignored legacy flag values and managed requirements, personality opt-out behavior with the flag absent or set to either value, role overrides, and preservation of explicit base instructions, including empty strings.

GitOrigin-RevId: 4e12c66b42bfc59d6f151a5b3c28fadc6654ae99

codex-rs/app-server-protocol/schema/json/ServerNotification.json

@@ -3250,6 +3250,7 @@
       ]
     },
     "Personality": {
+      "description": "Deprecated: `friendly` and `pragmatic` no longer select a style.",
       "enum": [
         "none",
         "friendly",
@@ -5983,7 +5984,8 @@
             {
               "type": "null"
             }
-          ]
+          ],
+          "description": "@deprecated Reports the saved setting; `friendly` and `pragmatic` no longer select a style."
         },
         "sandboxPolicy": {
           "$ref": "#/definitions/SandboxPolicy"