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/app.py

@@ -750,12 +750,11 @@ def display_preview_generator():
     
     # 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:
-        from src.display_geometry import logical_size
         width, height = logical_size(config_manager.load_config())
     except (KeyError, TypeError, ValueError, AttributeError, ConfigError):
-        width = 128
-        height = 64
+        width, height = logical_size({})
     
     while True:
         try: