Initial project structure

Scaffold all modules, route stubs, data models, and config.
No logic implemented yet — all core methods raise NotImplementedError.
Establishes the full directory layout matching the architecture in CLAUDE.md.

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

fellowship/core/rectifier.py

@@ -0,0 +1,41 @@
+"""
+History rectifier — manages slot reservation and message insertion ordering.
+Ensures a bot's response appears at the correct logical position in history
+even when talker messages arrive during LLM generation.
+"""
+
+import logging
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from fellowship.core.session import Session, Message
+
+logger = logging.getLogger(__name__)
+
+
+class HistoryRectifier:
+    def __init__(self, session: "Session") -> None:
+        self.session = session
+
+    def reserve_slot(self, sender: str, turn: int) -> int:
+        """
+        Append a placeholder Message (content=None) to history.
+        Returns the index of the reserved slot.
+        Called immediately before an LLM call is dispatched.
+        """
+        raise NotImplementedError
+
+    def fill_slot(self, index: int, content: str, tokens: int) -> None:
+        """
+        Fill the reserved slot at the given index with the completed response.
+        Called when the LLM call returns.
+        """
+        raise NotImplementedError
+
+    def insert_after_slot(self, slot_index: int, message: "Message") -> None:
+        """
+        Insert a talker message after the given slot index.
+        Called when a talker message arrives while a slot is reserved.
+        Subsequent messages increment their positions accordingly.
+        """
+        raise NotImplementedError