feat: implement CRM and tax accounting specialized services and repositories

Phase 2: Repository Implementation (Dapper)
- TaxProfileRepository: tax profile CRUD + risk level analysis + filing due dates
- TaxFilingScheduleRepository: schedule tracking + upcoming due dates + completion marking
- ConsultingActivityRepository: CRM activity history + pending followups + consultant tracking
- ContractRepository: contract lifecycle + active contracts + expiring alerts + MRR calculation
- RevenueTrackingRepository: invoice tracking + payment status + revenue analysis

Phase 3: Service Layer (Business Logic)
- TaxProfileService: profile creation, risk assessment, upcoming filing detection
- TaxFilingScheduleService: schedule management, deadline tracking, completion workflow
- ConsultingActivityService: activity logging, followup management, consultant productivity
- ContractService: contract management, MRR calculation, expiring contract alerts
- RevenueTrackingService: invoice creation, payment tracking, revenue analytics

Phase 4: API Controller (REST Endpoints)
- TaxProfileController: CRUD operations + high-risk filtering + upcoming filings query

Architecture Highlights:
- SOLID principles: each layer has clear responsibility
- Dapper-based repositories for data access
- Comprehensive service layer for business logic
- RESTful API design with proper error handling
- Ready for Blazor UI implementation and deployment

Database Migration V015 executed:
- 5 new specialized tables for CRM and tax accounting
- Appropriate indexes for query performance
- Foreign key constraints for data integrity

TaxBaik.Infrastructure/Repositories/TaxFilingScheduleRepository.cs

@@ -0,0 +1,73 @@
+namespace TaxBaik.Infrastructure.Repositories;
+
+using Dapper;
+using TaxBaik.Domain.Entities;
+using TaxBaik.Domain.Interfaces;
+
+public class TaxFilingScheduleRepository(IDbConnectionFactory connectionFactory) : BaseRepository(connectionFactory), ITaxFilingScheduleRepository
+{
+    public async Task<int> CreateAsync(TaxFilingSchedule schedule, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryFirstAsync<int>(
+            @"INSERT INTO tax_filing_schedules (client_id, filing_type, due_date, filing_year, status, assigned_to, notes, created_at, updated_at)
+              VALUES (@ClientId, @FilingType, @DueDate, @FilingYear, @Status, @AssignedToId, @Notes, NOW(), NOW())
+              RETURNING id",
+            schedule);
+    }
+
+    public async Task<TaxFilingSchedule?> GetByIdAsync(int id, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryFirstOrDefaultAsync<TaxFilingSchedule>(
+            @"SELECT id, client_id, filing_type, due_date, filing_year, status, assigned_to, completed_date, notes, created_at, updated_at
+              FROM tax_filing_schedules WHERE id = @Id",
+            new { Id = id });
+    }
+
+    public async Task<IEnumerable<TaxFilingSchedule>> GetByClientIdAsync(int clientId, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryAsync<TaxFilingSchedule>(
+            @"SELECT id, client_id, filing_type, due_date, filing_year, status, assigned_to, completed_date, notes, created_at, updated_at
+              FROM tax_filing_schedules WHERE client_id = @ClientId ORDER BY due_date DESC",
+            new { ClientId = clientId });
+    }
+
+    public async Task<IEnumerable<TaxFilingSchedule>> GetUpcomingDuesAsync(int daysAhead = 30, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryAsync<TaxFilingSchedule>(
+            @"SELECT id, client_id, filing_type, due_date, filing_year, status, assigned_to, completed_date, notes, created_at, updated_at
+              FROM tax_filing_schedules
+              WHERE status = 'pending' AND due_date BETWEEN CURRENT_DATE AND CURRENT_DATE + INTERVAL '1 day' * @DaysAhead
+              ORDER BY due_date ASC",
+            new { DaysAhead = daysAhead });
+    }
+
+    public async Task<IEnumerable<TaxFilingSchedule>> GetByStatusAsync(string status, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        return await conn.QueryAsync<TaxFilingSchedule>(
+            @"SELECT id, client_id, filing_type, due_date, filing_year, status, assigned_to, completed_date, notes, created_at, updated_at
+              FROM tax_filing_schedules WHERE status = @Status ORDER BY due_date",
+            new { Status = status });
+    }
+
+    public async Task UpdateAsync(TaxFilingSchedule schedule, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        await conn.ExecuteAsync(
+            @"UPDATE tax_filing_schedules SET filing_type = @FilingType, due_date = @DueDate, status = @Status,
+              assigned_to = @AssignedToId, notes = @Notes, updated_at = NOW() WHERE id = @Id",
+            schedule);
+    }
+
+    public async Task MarkCompletedAsync(int id, CancellationToken cancellationToken = default)
+    {
+        using var conn = Conn();
+        await conn.ExecuteAsync(
+            @"UPDATE tax_filing_schedules SET status = 'completed', completed_date = NOW(), updated_at = NOW() WHERE id = @Id",
+            new { Id = id });
+    }
+}