refactor: reorganize into monorepo with separate subprojects

Structure webber into three independent subprojects:
- webber-api/: FastAPI backend server with all agent code
- webber-cli/: Standalone CLI client (renamed from cli/ to webber_cli/)
- webber-sandbox/: Test project for functional testing

Key changes:
- Each subproject has its own .venv (Python 3.12+)
- Added sandbox.sh for managing test project templates
- Created sandbox-templates/ with calculator-cli and empty starter
- Updated CI/CD for prefixed tags (api/v*, cli/v*)
- Added comprehensive AGENTS.md with operational instructions
- Added gitignore filtering to glob and grep tools
- Created pyproject.toml for each subproject

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-api/src/cli/session/context.py

@@ -0,0 +1,60 @@
+"""
+Session state management.
+"""
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Literal
+
+
+@dataclass
+class Message:
+    """Single message in conversation history."""
+    role: Literal["user", "assistant", "system"]
+    content: str
+    timestamp: datetime = field(default_factory=datetime.now)
+
+    def __str__(self) -> str:
+        return f"[{self.role}] {self.content[:50]}..."
+
+
+@dataclass
+class SessionState:
+    """
+    Persistent state for a CLI session.
+
+    Tracks conversation history and context.
+    """
+    working_dir: str
+    messages: list[Message] = field(default_factory=list)
+    started_at: datetime = field(default_factory=datetime.now)
+
+    # Token tracking (for future context management)
+    estimated_tokens: int = 0
+    max_tokens: int = 128000
+
+    def add_message(self, role: Literal["user", "assistant", "system"], content: str) -> None:
+        """Add a message to history."""
+        self.messages.append(Message(role=role, content=content))
+        # Rough token estimate (4 chars per token)
+        self.estimated_tokens += len(content) // 4
+
+    def get_history(self, limit: int | None = None) -> list[Message]:
+        """Get recent message history."""
+        if limit:
+            return self.messages[-limit:]
+        return self.messages
+
+    def clear_history(self) -> None:
+        """Clear message history."""
+        self.messages.clear()
+        self.estimated_tokens = 0
+
+    @property
+    def message_count(self) -> int:
+        """Number of messages in history."""
+        return len(self.messages)
+
+    @property
+    def is_near_limit(self) -> bool:
+        """Check if approaching token limit."""
+        return self.estimated_tokens > (self.max_tokens * 0.8)