Add milestone_type field to milestone queries that indicates whether
a milestone is a start milestone ('start') or finish milestone ('finish').
Changes:
- Add milestone_type column to activities table schema
- Parse milestone_type from XER TASK table (MS_Start/MS_Finish)
- Include milestone_type in list_milestones response
- Update contract tests for milestone_type field
- Update specs, contracts, and documentation
The milestone_type is determined by:
1. Explicit milestone_type field in XER (MS_Start -> 'start', MS_Finish -> 'finish')
2. Derived from task_type (TT_Mile -> 'start', TT_FinMile -> 'finish')
Add computed driving flag to all relationship queries (list_relationships,
get_predecessors, get_successors). A relationship is marked as driving when
the predecessor's early end date plus lag determines the successor's early
start date.
Changes:
- Add early_start_date and early_end_date columns to activities schema
- Parse early dates from TASK table in XER files
- Implement is_driving_relationship() helper with 24hr tolerance for
calendar gaps
- Update all relationship queries to compute and return driving flag
- Add contract and unit tests for driving flag functionality
- Update spec, contracts, and documentation
