fix(proxy): use long-poll for HA frontend shim

[Ruffo324]

Summary

• add configurable frontend_proxy_transport for the injected HA frontend WebSocket shim
• default the HA frontend shim to long_poll to avoid fragile streaming fetch/SSE failures through restrictive browsers/proxies
• preserve sse/poll as configurable options
• add regression coverage ensuring bridge /v1 routes remain reserved under frontend proxy at /

Tests

• pnpm exec vitest run packages/proxy/tests/httpServer.test.ts
• pnpm exec tsc -p packages/proxy/tsconfig.json --noEmit
• pnpm exec biome check packages/proxy/src/transports/frontendProxy.ts packages/proxy/src/config/serverConfig.ts packages/proxy/tests/httpServer.test.ts addons/https2wss/config.yaml addons/https2wss/translations/en.yaml
• pnpm -w build