feat: goal-based savings tracking & milestones (bounty #133)

[alexanderxfgl-bit]

Bounty Claim: $250 — Issue #133

Implementation

Full savings goal tracking system with auto-milestones, contributions, and progress monitoring.

Backend Changes

Models (app/models.py):

• SavingsGoalStatus enum: active → completed / abandoned
• SavingsGoal: name, target_amount, current_amount, currency, deadline, status
• SavingsMilestone: goal_id, name, target_amount, reached_at
• SavingsContribution: goal_id, amount, contributed_at, notes

Service (app/services/savings.py):

• create_goal() — with auto-milestone creation at 25%/50%/75%/100% thresholds
• add_contribution() — deposit tracking with auto-completion detection
• _check_milestones() — marks milestones as reached when current_amount crosses threshold
• get_goal_progress() — percent complete, remaining amount, days remaining
• mark_goal_completed() / abandon_goal() — status transitions
• parse_amount() — Decimal validation for all money inputs

Routes (app/routes/savings.py):

• POST /savings — create goal with validation
• GET /savings — list goals with optional status filter
• GET /savings/<id> — get goal with progress stats
• PATCH /savings/<id> — update goal (name, target, deadline, status)
• DELETE /savings/<id> — delete goal with cascading milestones/contributions
• POST /savings/<id>/contributions — add contribution
• GET /savings/<id>/contributions — list contributions
• GET /savings/<id>/milestones — list milestones
• POST /savings/<id>/complete — manually complete goal
• POST /savings/<id>/abandon — abandon goal

Schema (app/db/schema.sql):

• savings_goals, savings_milestones, savings_contributions tables
• savings_goal_status enum type
• Indexes for efficient user/status and goal/contributed_at queries

Tests

12 tests covering:

• Goal CRUD (create, list, get, delete)
• Input validation (missing name, negative amounts)
• Deadline handling
• Contribution workflow (add, validate, list)
• Auto-milestone creation (4 milestones per goal)
• Goal completion and abandonment

Closes #133