feat: task 1.3 vite dev proxy + tsconfig hardening

Same-origin dev proxy via Vite's server.proxy:
- /api/*       -> ${VITE_DEV_DIRECTUS_URL}/*   (Directus REST + GraphQL)
- /ws-business -> ws://.../websocket           (Directus business-plane WS)
- /ws-live     -> ${VITE_DEV_PROCESSOR_WS_URL} (Processor live WS, Phase 1.5)

WS proxy targets derive ws:// scheme from the http(s) Directus URL.
loadEnv reads VITE_DEV_* overrides; sensible localhost defaults.

tsconfig.app.json: noUncheckedIndexedAccess + noImplicitOverride.

.env.example documents the two override vars; .env.local is gitignored
via the existing *.local pattern.

README "Local dev" section: proxy table + override instructions + port
collision workaround.

Deviation: spec called for .env.dev.example/.env.dev.local but Vite's
dev mode is "development" not "dev", so mode-specific files would be
.env.development.* and Vite wouldn't auto-load .env.dev.local. Switched
to the standard Vite .env.example/.env.local convention. Documented in
the task's Done section.

Plus: backfill 1.2 commit SHA (9918418) in its Done section.

tsconfig.app.json

@@ -24,7 +24,9 @@
     "noUnusedLocals": true,
     "noUnusedParameters": true,
     "erasableSyntaxOnly": true,
-    "noFallthroughCasesInSwitch": true
+    "noFallthroughCasesInSwitch": true,
+    "noUncheckedIndexedAccess": true,
+    "noImplicitOverride": true
   },
   "include": ["src"]
 }