refactor: replace source._outcome cross-class access with public outcome property

`_FullscreenPeek._build_header` was reading `source._outcome` directly on
a `_LivePanelBase` instance, crossing class boundaries into a private
attribute.  Expose an `outcome` property on `_LivePanelBase` (matching
the `iteration_id` property added in ef9a178 for the parallel case) so
the fullscreen header reads the value through a public API.  Same
observable behavior; the attribute is still the single source of truth
inside `freeze`.

Co-authored-by: Ralphify <noreply@ralphify.co>

Author: 2 people

src/ralphify/_console_emitter.py

@@ -353,6 +353,11 @@ def freeze(self, outcome: str) -> None:
             self._end = time.monotonic()
         self._outcome = outcome
 
+    @property
+    def outcome(self) -> str | None:
+        """The frozen-iteration outcome label, or ``None`` while live."""
+        return self._outcome
+
     # ── Scroll buffer management ─────────────────────────────────────
 
     def add_scroll_line(self, markup: str) -> None:
@@ -830,7 +835,7 @@ def _build_header(self, total: int, visible: int) -> Text:
                 header.append("live", style=f"italic {_brand.GREEN}")
             else:
                 source = self._source
-                outcome = source._outcome if source is not None else None
+                outcome = source.outcome if source is not None else None
                 if outcome:
                     header.append("  ·  ", style="dim")
                     header.append(outcome, style=f"italic {_brand.LAVENDER}")