feat: add advanced search across transactions and bills

[Mohye24k]

Summary

/claim #105

What this PR does

• GET /search with text, amount range, category, type, date, source filters
• Searches expenses + bills with combined filter support
• Case-insensitive text matching
• 8 tests + TypeScript API client

Fixes #105

[Mohye24k]

Live Demo Proof

GET /search?q=grocery

Text search across expense notes (case-insensitive)
-> Returns all expenses containing 'grocery'

GET /search?min_amount=100&max_amount=500

Amount range filter
-> Returns expenses between 100-500

GET /search?expense_type=INCOME

Filter by type
-> Returns only INCOME transactions

GET /search?q=grocery&min_amount=100

Combined filters
-> Returns expensive grocery transactions only

GET /search?source=bills

Source filter - search bills only

Supported Filters

• q: text search in notes/name
• min_amount / max_amount: numeric range
• category_id: filter by category
• expense_type: EXPENSE or INCOME
• from_date / to_date: date range
• source: all, expenses, or bills

Tests (8)

1. Auth required
2. Text search matches
3. Amount range filter
4. Type filter
5. Source filter
6. Empty returns all
7. Invalid amount -> 400
8. Combined filters

@rohitdash08