add version display in UI sidebar + version bump rules

- VERSION file at repo root (0.3.0)
- vite.config.ts reads VERSION at build time, injects __OIKOS_VERSION__
- App.svelte shows version in sidebar tooltip + subtle text below logo
- AGENTS.md §9: every commit to main MUST bump VERSION
  (patch=bugfix, minor=new features, major=breaking changes)

web/vite.config.ts

@@ -1,6 +1,9 @@
 import { svelte } from '@sveltejs/vite-plugin-svelte'
 import tailwindcss from '@tailwindcss/vite'
 import { defineConfig } from 'vite'
+import { readFileSync } from 'fs'
+
+const version = readFileSync('../VERSION', 'utf-8').trim()
 
 // Injects OIKOS_API_TOKEN into proxied /api requests in dev — the API no
 // longer has a dev-open bypass (plans/2026-07-12-wails-desktop-app.md 0.4),
@@ -21,6 +24,9 @@ function authProxy(target: string, rewrite?: (path: string) => string) {
 export default defineConfig({
   plugins: [tailwindcss(), svelte()],
   base: '/',
+  define: {
+    __OIKOS_VERSION__: JSON.stringify(`v${version}`),
+  },
   resolve: {
     alias: { $lib: '/src/lib' }
   },