feat: WP-0001 foundation + WP-0002 core extensions

WP-0001 — Foundation & GAAF Baseline
- SCOPE.md, ARCHITECTURE-LAYERS.md, contracts/ tree
- .claude/rules/ stubs filled (architecture, stack, boundary)
- 57 tests (pytest), pyproject.toml with ruff+mypy, CI workflow

WP-0002 — Core Extensions (FR-4 + FR-3)
- FR-4: BudgetTracker (thread-safe) + LLMBudgetExceededError +
  optional RunConfig.budget_tracker + enforcement in all adapters
- FR-3: async_execute_prompt on LLMAdapter ABC (asyncio.to_thread
  fallback) + native asyncio.create_subprocess_exec in ClaudeCodeAdapter

81 tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

llm_connect/exceptions.py

@@ -64,6 +64,30 @@ class LLMTimeoutError(LLMError):
     pass
 
 
+class LLMBudgetExceededError(LLMError):
+    """Token budget cap exceeded during a call or delegation chain.
+
+    Attributes:
+        total: The configured token cap.
+        spent: Tokens already consumed before this call.
+        requested: Tokens this call would have consumed.
+    """
+
+    def __init__(
+        self,
+        message: str,
+        total: int = 0,
+        spent: int = 0,
+        requested: int = 0,
+        cause: Optional[Exception] = None,
+        context: Optional[Dict[str, Any]] = None,
+    ):
+        super().__init__(message, cause=cause, context=context)
+        self.total = total
+        self.spent = spent
+        self.requested = requested
+
+
 class LLMSubprocessError(LLMError):
     """Claude Code CLI subprocess failed.