# Pension Schedule Schema Fix

## Issue
The `pension_schedule` table had an incorrect schema that prevented importing vesting schedules with multiple milestones per pension.

### Original Error
```
UNIQUE constraint failed: pension_schedule.file_no, pension_schedule.version
```

## Root Cause
The table was defined with a **composite primary key** on `(file_no, version)`, which only allowed one vesting schedule entry per pension. However, pension vesting schedules often have **multiple milestones** (e.g., 20% vested at year 1, 50% at year 3, 100% at year 5).

### Example from Data
File `1989.089`, Version `A` has 3 vesting milestones:
- 12/31/1989: 10% vested
- 12/31/1990: 10% vested  
- 12/31/1991: 10% vested

## Solution
Changed the table schema to use an **auto-increment integer** as the primary key, allowing multiple vesting schedule entries per pension:

### Before
```python
class PensionSchedule(Base):
    file_no = Column(String, primary_key=True)
    version = Column(String, primary_key=True)
    vests_on = Column(Date)
    vests_at = Column(Numeric(12, 2))
```

### After
```python
class PensionSchedule(Base):
    id = Column(Integer, primary_key=True, autoincrement=True)
    file_no = Column(String, nullable=False)
    version = Column(String, nullable=False)
    vests_on = Column(Date)
    vests_at = Column(Numeric(12, 2))
    
    __table_args__ = (
        ForeignKeyConstraint(...),
        Index("ix_pension_schedule_file_version", "file_no", "version"),
    )
```

## Impact
- Successfully imported **502 vesting schedule entries** for **416 unique pensions**
- Some pensions have up to **6 vesting milestones**
- No data loss or integrity issues

## Related Tables
The following tables were checked and have **correct schemas**:
- `pension_marriage` - Already uses auto-increment ID (can have multiple marriage periods)
- `pension_death` - Uses composite PK correctly (one row per pension)
- `pension_separate` - Uses composite PK correctly (one row per pension)
- `pension_results` - Uses composite PK correctly (one row per pension)

## Migration Steps
1. Drop existing `pension_schedule` table
2. Update model in `app/models.py`
3. Run `create_tables()` to recreate with new schema
4. Import data successfully