Feature/stream agent replies

[xing139565]

Summary

• add realtime channel message update events for agent reply streaming
• stream runtime text into pending channel replies
• reveal streamed agent messages progressively in the chat UI
• hide pending dots once streamed content has finished displaying

Tests

• AGENT_SPACE_TEST_DATABASE_URL=postgres://localhost/agent_space_test node node_modules/vitest/vitest.mjs run features/chat/chat-primitives.test.tsx
• npm --prefix apps/web run typecheck:test
• npm run typecheck:deps
• npm run typecheck:daemon
• git diff --check