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/services/__init__.py

@@ -0,0 +1,45 @@
+"""Services layer for business logic."""
+
+from .session_service import (
+    get_active_session,
+    set_active_session,
+    clear_active_session,
+    get_active_session_path,
+    validate_no_other_active_session,
+)
+from .project_service import (
+    create_project,
+    get_project,
+    update_project,
+    list_projects,
+    get_projects_root,
+    ensure_project_structure,
+)
+from .note_service import (
+    add_note,
+    consolidate_notes,
+)
+from .heuristics_service import (
+    suggest_next_steps,
+)
+from .summary_service import (
+    generate_summary,
+)
+
+__all__ = [
+    "get_active_session",
+    "set_active_session",
+    "clear_active_session",
+    "get_active_session_path",
+    "validate_no_other_active_session",
+    "create_project",
+    "get_project",
+    "update_project",
+    "list_projects",
+    "get_projects_root",
+    "ensure_project_structure",
+    "add_note",
+    "consolidate_notes",
+    "suggest_next_steps",
+    "generate_summary",
+]