feat(android): Capacitor wrapper bundling the Fabric web frontend

Greenfield Android client built as a Capacitor shell (mirrors the
Desktop strategy — reuses the React SPA 100%):
- appId ai.hangman.fabric, appName Fabric, androidScheme http +
  usesCleartextTraffic (talks to the http Center/Guild backends; the
  login screen sets the Center base, so a phone points at a LAN/host
  URL instead of localhost).
- scripts/build-web.mjs builds Fabric.Frontend and copies dist -> www;
  npm run sync / apk:debug wire it to Gradle.
- Native android/ project (cap add android) committed; build outputs,
  www/, node_modules, local.properties gitignored.
- Launcher icons = the Fabric mark (adaptive: green mark on black,
  legacy + round) at all densities.

Verified: gradlew assembleDebug -> app-debug.apk (4.2MB) containing
assets/public/index.html + the SPA bundle + Fabric icons.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/build-web.mjs

@@ -0,0 +1,37 @@
+#!/usr/bin/env node
+/**
+ * Build the Fabric web frontend and copy the static bundle into www/ so the
+ * Capacitor Android app ships it. Capacitor serves www/ from http://localhost
+ * with SPA index.html fallback, so the standard (absolute-base) build +
+ * BrowserRouter work as-is.
+ *
+ * Fabric.Frontend is the sibling submodule under the parent Fabric repo.
+ */
+import { execSync } from 'node:child_process'
+import fs from 'node:fs'
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+const ROOT = path.resolve(__dirname, '..')
+const FRONTEND = path.resolve(ROOT, '..', 'Fabric.Frontend')
+const SRC = path.join(FRONTEND, 'dist')
+const DEST = path.join(ROOT, 'www')
+
+if (!fs.existsSync(FRONTEND)) {
+  console.error(`[build-web] Fabric.Frontend not found at ${FRONTEND}`)
+  process.exit(1)
+}
+
+console.log('[build-web] building frontend…')
+execSync('npm install --no-audit --no-fund', { cwd: FRONTEND, stdio: 'inherit' })
+execSync('npm run build', { cwd: FRONTEND, stdio: 'inherit' })
+
+if (!fs.existsSync(path.join(SRC, 'index.html'))) {
+  console.error(`[build-web] expected ${SRC}/index.html after build`)
+  process.exit(1)
+}
+
+fs.rmSync(DEST, { recursive: true, force: true })
+fs.cpSync(SRC, DEST, { recursive: true })
+console.log(`[build-web] copied ${SRC} -> ${DEST}`)