feat(core): StreamingChatAdapter for token-by-token Anthropic relay (#503)

## Summary

- `StreamingChatAdapter` in `codeframe/core/adapters/streaming_chat.py` wraps `anthropic.AsyncAnthropic().messages.stream()` and yields typed `ChatEvent` objects
- Replaces the echo stub in `session_chat_ws.py` (`_run_streaming_adapter`) with the real adapter
- Safe read-only tool set for interactive sessions: `read_file`, `list_files`, `search_codebase`
- History load/persist via `InteractiveSessionRepository`; tiktoken-based context truncation
- 18 unit tests; all 8 acceptance criteria from #503 verified

Closes #503

Author: frankbria

codeframe/core/adapters/__init__.py

@@ -1,3 +1,9 @@
+from codeframe.core.adapters.streaming_chat import (
+    ChatEvent,
+    ChatEventType,
+    StreamingChatAdapter,
+    STREAMING_SAFE_TOOLS,
+)
 from codeframe.core.adapters.agent_adapter import (
     AdapterTokenUsage,
     AgentAdapter,
@@ -17,6 +23,10 @@
 from codeframe.core.adapters.verification_wrapper import VerificationWrapper
 
 __all__ = [
+    "ChatEvent",
+    "ChatEventType",
+    "StreamingChatAdapter",
+    "STREAMING_SAFE_TOOLS",
     "AdapterTokenUsage",
     "AgentAdapter",
     "AgentContext",