fix: address CodeRabbit review on #580

- Preview fallbacks (SSE stream and /display/current) use logical_size({})
  (128x32, the shared default) instead of a hard-coded 128x64.
- display_geometry treats a non-mapping display/hardware block as missing,
  so a malformed config.json falls back to defaults instead of raising
  AttributeError (which turned the Starlark render into an HTTP 500).
- Docs: the static update interval falls back manifest -> plugin config
  -> 60s, in both the API reference and the architecture spec.

Not taken: validating double_sided copies against chain_length/parallel.
An orientation Rotate: or U-mapper pixel mapper decides which axis panels
lie on, so the counts would reject working setups (the existing
vertical-split test is one).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web_interface/blueprints/api_v3/display.py

@@ -27,16 +27,12 @@ def get_display_current():
 
         # Get display dimensions from config: the logical size DisplayManager
         # renders at, so double-sided setups preview one screen
+        from src.display_geometry import logical_size
         try:
-            if api_v3.config_manager:
-                from src.display_geometry import logical_size
-                width, height = logical_size(api_v3.config_manager.load_config())
-            else:
-                width = 128
-                height = 64
+            config = api_v3.config_manager.load_config() if api_v3.config_manager else {}
+            width, height = logical_size(config)
         except Exception:
-            width = 128
-            height = 64
+            width, height = logical_size({})
 
         # Try to read snapshot file
         image_data = None