feat: implement XER MCP Server with 9 schedule query tools

Implement complete MCP server for parsing Primavera P6 XER files and
exposing schedule data through MCP tools. All 4 user stories complete.

Tools implemented:
- load_xer: Parse XER files into SQLite database
- list_activities: Query activities with pagination and filtering
- get_activity: Get activity details by ID
- list_relationships: Query activity dependencies
- get_predecessors/get_successors: Query activity relationships
- get_project_summary: Project overview with counts
- list_milestones: Query milestone activities
- get_critical_path: Query driving path activities

Features:
- Tab-delimited XER format parsing with pluggable table handlers
- In-memory SQLite database for fast queries
- Pagination with 100-item default limit
- Multi-project file support with project selection
- ISO8601 date formatting
- NO_FILE_LOADED error handling for all query tools

Test coverage: 81 tests (contract, integration, unit)

src/xer_mcp/models/__init__.py

@@ -0,0 +1,17 @@
+"""Data models for XER MCP Server."""
+
+from xer_mcp.models.activity import Activity
+from xer_mcp.models.calendar import Calendar
+from xer_mcp.models.pagination import PaginationMetadata
+from xer_mcp.models.project import Project
+from xer_mcp.models.relationship import Relationship
+from xer_mcp.models.wbs import WBS
+
+__all__ = [
+    "Activity",
+    "Calendar",
+    "PaginationMetadata",
+    "Project",
+    "Relationship",
+    "WBS",
+]

src/xer_mcp/models/activity.py

@@ -0,0 +1,23 @@
+"""Activity data model."""
+
+from dataclasses import dataclass
+from datetime import datetime
+
+
+@dataclass
+class Activity:
+    """A unit of work in the schedule."""
+
+    task_id: str
+    proj_id: str
+    task_code: str
+    task_name: str
+    task_type: str
+    wbs_id: str | None = None
+    target_start_date: datetime | None = None
+    target_end_date: datetime | None = None
+    act_start_date: datetime | None = None
+    act_end_date: datetime | None = None
+    total_float_hr_cnt: float | None = None
+    driving_path_flag: bool = False
+    status_code: str | None = None

src/xer_mcp/models/calendar.py

@@ -0,0 +1,13 @@
+"""Calendar data model (internal use only)."""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Calendar:
+    """Work schedule definition. Not exposed via MCP tools."""
+
+    clndr_id: str
+    clndr_name: str
+    day_hr_cnt: float | None = None
+    week_hr_cnt: float | None = None

src/xer_mcp/models/pagination.py

@@ -0,0 +1,13 @@
+"""Pagination metadata model."""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class PaginationMetadata:
+    """Response wrapper for paginated queries."""
+
+    total_count: int
+    offset: int
+    limit: int
+    has_more: bool

src/xer_mcp/models/project.py

@@ -0,0 +1,15 @@
+"""Project data model."""
+
+from dataclasses import dataclass
+from datetime import datetime
+
+
+@dataclass
+class Project:
+    """Top-level container representing a P6 project."""
+
+    proj_id: str
+    proj_short_name: str
+    plan_start_date: datetime | None = None
+    plan_end_date: datetime | None = None
+    loaded_at: datetime | None = None

src/xer_mcp/models/relationship.py

@@ -0,0 +1,14 @@
+"""Relationship data model."""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Relationship:
+    """A dependency link between two activities."""
+
+    task_pred_id: str
+    task_id: str
+    pred_task_id: str
+    pred_type: str
+    lag_hr_cnt: float = 0.0

src/xer_mcp/models/wbs.py

@@ -0,0 +1,14 @@
+"""Work Breakdown Structure (WBS) data model."""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class WBS:
+    """Hierarchical organization of activities."""
+
+    wbs_id: str
+    proj_id: str
+    wbs_short_name: str
+    parent_wbs_id: str | None = None
+    wbs_name: str | None = None