perf: hot-path micro fixes in the render loop (#403)

* perf: hot-path micro fixes in the render loop

- _check_wifi_status_message stat'd the status file on every render
  iteration (60+ fps) for a message whose lifetime is seconds; throttle
  the check to 1 Hz with a cached result.
- Demote the per-iteration "Display active, processing mode" INFO to
  DEBUG and convert the remaining eager f-string logs to lazy % args —
  the devpi baseline showed ~9 journald lines/sec, which is both noise
  and SD-card wear.
- Vegas cycle-end blank frame: hoist the inline PIL import and reuse a
  preallocated buffer instead of allocating per cycle wrap.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FqzC1nzTWL4kaqgMaQZFam

* fix: initialise wifi-status throttle state in __init__

Codacy (pylint access-member-before-definition) on #403: the throttled
early-return read _wifi_status_last_result relying on the non-local
invariant that the first call always passes the throttle window and
assigns it. Correct at runtime, but fragile — initialise both throttle
fields in the constructor and drop the getattr fallback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FqzC1nzTWL4kaqgMaQZFam

---------

Co-authored-by: Chuck <chuck@example.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/vegas_mode/render_pipeline.py

@@ -66,6 +66,10 @@ class RenderPipeline:
             else display_manager.height
         )
 
+        # Reusable blank frame for cycle-end pushes (allocated lazily,
+        # re-blacked before each reuse)
+        self._blank_frame = None
+
         # ScrollHelper for optimized scrolling
         self.scroll_helper = ScrollHelper(
             self.display_width,
@@ -234,11 +238,19 @@ class RenderPipeline:
                     )
                     # Push blank immediately so the hardware never shows any
                     # post-wrap content while the coordinator recomposes the
-                    # next cycle (~100 ms).
+                    # next cycle (~100 ms). The blank is allocated once and
+                    # reused across cycle wraps (fresh paste each time in case
+                    # a consumer drew on the previous one).
                     try:
-                        from PIL import Image as _Image
-                        blank = _Image.new('RGB', (self.display_width, self.display_height))
-                        self.display_manager.image = blank
+                        if self._blank_frame is None or self._blank_frame.size != (
+                                self.display_width, self.display_height):
+                            self._blank_frame = Image.new(
+                                'RGB', (self.display_width, self.display_height))
+                        else:
+                            self._blank_frame.paste(
+                                (0, 0, 0),
+                                (0, 0, self.display_width, self.display_height))
+                        self.display_manager.image = self._blank_frame
                         self.display_manager.update_display()
                     except Exception:
                         logger.exception("Failed to write blank frame to display at cycle end")