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/context.py

@@ -0,0 +1,42 @@
+"""
+Context manager — assembles the conversation history for a bot's prompt.
+Ensures bots only see messages, never foreign system prompts.
+Handles context summarization when enabled.
+"""
+
+import logging
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from fellowship.core.session import Session, BotConfig
+
+logger = logging.getLogger(__name__)
+
+
+class ContextManager:
+    def __init__(self, session: "Session") -> None:
+        self.session = session
+
+    def build_context(self, bot: "BotConfig") -> list[dict]:
+        """
+        Return the conversation history formatted as LLM messages for the given bot.
+        Uses shared_context or scoped_context based on session options.
+        Skips any slots with content=None (reserved but not yet filled).
+        """
+        raise NotImplementedError
+
+    def estimate_tokens(self, messages: list[dict]) -> int:
+        """
+        Estimate total token count for a list of messages.
+        Used to check against max_context_tokens.
+        """
+        raise NotImplementedError
+
+    async def summarize(self) -> None:
+        """
+        Summarize the older portion of history to reduce context size.
+        Retains a recent tail of messages intact.
+        Stores the summary in session state; future context builds use summary + tail.
+        Full history list is preserved unchanged.
+        """
+        raise NotImplementedError