Sync collaboration mode naming across Default prompt, tools, and TUI (#10666)

## Summary
- add shared `ModeKind` helpers for display names, TUI visibility, and
`request_user_input` availability
- derive TUI mode filtering/labels from shared `ModeKind` metadata
instead of local hardcoded matches
- derive `request_user_input` availability text and unavailable error
mode names from shared mode metadata
- replace hardcoded known mode names in the Default collaboration-mode
template with `{{KNOWN_MODE_NAMES}}` and fill it from
`TUI_VISIBLE_COLLABORATION_MODES`
- add regression tests for mode metadata sync and placeholder
replacement

## Notes
- `cargo test -p codex-core` integration target (`tests/all`) still
shows pre-existing env-specific failures in this environment due missing
`test_stdio_server` binary resolution; core unit tests are green.

## Codex author
`codex resume 019c26ff-dfe7-7173-bc04-c9e1fff1e447`

codex-rs/protocol/src/config_types.rs

@@ -193,6 +193,27 @@ pub enum ModeKind {
     Execute,
 }
 
+pub const TUI_VISIBLE_COLLABORATION_MODES: [ModeKind; 2] = [ModeKind::Default, ModeKind::Plan];
+
+impl ModeKind {
+    pub const fn display_name(self) -> &'static str {
+        match self {
+            Self::Plan => "Plan",
+            Self::Default => "Default",
+            Self::PairProgramming => "Pair Programming",
+            Self::Execute => "Execute",
+        }
+    }
+
+    pub const fn is_tui_visible(self) -> bool {
+        matches!(self, Self::Plan | Self::Default)
+    }
+
+    pub const fn allows_request_user_input(self) -> bool {
+        matches!(self, Self::Plan)
+    }
+}
+
 /// Collaboration mode for a Codex session.
 #[derive(Clone, PartialEq, Eq, Hash, Debug, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(rename_all = "lowercase")]
@@ -324,4 +345,17 @@ mod tests {
             assert_eq!(ModeKind::Default, mode);
         }
     }
+
+    #[test]
+    fn tui_visible_collaboration_modes_match_mode_kind_visibility() {
+        let expected = [ModeKind::Default, ModeKind::Plan];
+        assert_eq!(expected, TUI_VISIBLE_COLLABORATION_MODES);
+
+        for mode in TUI_VISIBLE_COLLABORATION_MODES {
+            assert!(mode.is_tui_visible());
+        }
+
+        assert!(!ModeKind::PairProgramming.is_tui_visible());
+        assert!(!ModeKind::Execute.is_tui_visible());
+    }
 }