Implement storage layer for MVP-1 Personal Tracker CLI

Add storage layer with FileStorage, MarkdownReader, and MarkdownWriter classes.
Add data models (Project, Session, Note, Change).

tracker/models/project.py

@@ -0,0 +1,21 @@
+"""Project model definition."""
+from pydantic import BaseModel, Field
+from datetime import datetime
+from typing import Optional
+
+
+class Project(BaseModel):
+    """Represents a tracked project."""
+
+    id: str
+    name: str
+    slug: str
+    description: str = ""
+    type: str = "misc"  # code, homelab, automation, agent, research, misc
+    status: str = "inbox"  # inbox, next, active, blocked, waiting, done, archived
+    tags: list[str] = Field(default_factory=list)
+    root_path: str = ""
+    repo_path: Optional[str] = None
+    created_at: datetime
+    updated_at: datetime
+    last_session_at: Optional[datetime] = None