perf(web): cache macro images in local PWA, bump to 1.1.2

Same fix as the relay: the local PWA re-fetched every macro image and revoked
the blob on each re-render. Cache image URL -> Promise<objectURL> and reuse
across renders (images are immutable per uuid path); add Cache-Control:
immutable on the desktop /api/image response. Verified in a browser: 7
re-renders produced only the initial 3 image fetches, none repeated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

config.py

@@ -1,6 +1,6 @@
 # Configuration and constants for MacroPad Server
 
-VERSION = "1.1.1"
+VERSION = "1.1.2"
 DEFAULT_PORT = 40000
 SETTINGS_FILE = "settings.json"