[CLAUDE] Domain+App+Api: Module Ngan sach (Budget) - 4 bang + workflow simple

User request: 'Them cho tao 4 bang luu ve ngan sach: Header / Chi tiet
/ Quy trinh duyet / Lich su thay doi'.

Domain (5 file + 1 enum):
 - Budget (header) — Aggregate root, AuditableEntity. Field: MaNganSach,
   TenNganSach, Description, NamNganSach, ProjectId FK, DepartmentId?,
   DrafterUserId, Phase (BudgetPhase 5-state), TongNganSach (sum auto
   tu Details), SlaDeadline, SlaWarningSent.
 - BudgetDetail — flat row pattern (GroupCode/GroupName + Item +
   KhoiLuong/DonGia/ThanhTien). 18,4 precision KhoiLuong, 18,2 money.
 - BudgetApproval — workflow history (FromPhase/ToPhase/Decision/Comment)
 - BudgetChangelog — audit log unified (EntityType: Header/Detail/Workflow)
 - BudgetPhase enum 5 state: DangSoanThao(1) → ChoCCM(2) → ChoCEO(3) →
   DaDuyet(4) | TuChoi(99)
 - BudgetPolicy hardcoded (no versioned WF, simple default per user
   confirm 'tam thoi don gian'): Drafter/DeptManager → CCM → CEO/
   AuthorizedSigner. Reject path back to DangSoanThao.

Migration 14 AddBudgets:
 - 4 bang moi: Budgets + BudgetDetails + BudgetApprovals + BudgetChangelogs
 - Index: Phase+IsDeleted, ProjectId, NamNganSach, SlaDeadline,
   MaNganSach unique filtered. Cascade delete child.
 - +2 cot FK ngoai bang (per user 'lien ket ca 3'):
   * Contracts.BudgetId Guid? + index
   * PurchaseEvaluations.BudgetId Guid? + index
   Cho phep doi chieu chi phi HD/PE vs ngan sach goi thau.

Application CQRS (BudgetFeatures.cs ~340 line):
 - CreateBudget + UpdateBudgetDraft + TransitionBudget + ListBudgets
   (filter Phase/Project/Year + search + paging) + GetBudget bundle
   (Header + Details + Approvals + Workflow summary)
 - DeleteBudget (only DangSoanThao/TuChoi)
 - AddBudgetDetail + UpdateBudgetDetail + DeleteBudgetDetail (auto
   recompute TongNganSach = sum Details.ThanhTien)
 - ListBudgetChangelogs

Api: BudgetsController 11 endpoint REST /api/budgets:
 - GET /  /{id}  /{id}/changelogs
 - POST /  /{id}/transitions  /{id}/details
 - PUT /{id}  /{id}/details/{detailId}
 - DELETE /{id}  /{id}/details/{detailId}

DbContext + IApplicationDbContext: 4 DbSet new (Budgets/Details/
Approvals/Changelogs).

MenuKeys + DbInitializer: 4 menu key (Budgets root + Bg_List/Create/
Pending leaves) seed dau order=27 'Ngan sach' icon Wallet. Auto-grant
admin permission via SeedAdminPermissionsAsync (MenuKeys.All).

MaNganSach format don gian 'NS-YYYYMM-NNNN' Random.Shared (chua atomic
sequence - user said 'tam thoi chua co').

Workflow chua versioned, hardcode BudgetPolicy.Default. Tuong lai admin
config qua UI: them BudgetWorkflowDefinition tables tuong tu PE.

src/Backend/SolutionErp.Api/Controllers/BudgetsController.cs

@@ -0,0 +1,94 @@
+using MediatR;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using SolutionErp.Application.Budgets;
+using SolutionErp.Application.Budgets.Dtos;
+using SolutionErp.Application.Common.Models;
+using SolutionErp.Domain.Budgets;
+using SolutionErp.Domain.Contracts;
+
+namespace SolutionErp.Api.Controllers;
+
+[ApiController]
+[Route("api/budgets")]
+[Authorize]
+public class BudgetsController(IMediator mediator) : ControllerBase
+{
+    [HttpGet]
+    public async Task<ActionResult<PagedResult<BudgetListItemDto>>> List(
+        [FromQuery] int page = 1, [FromQuery] int pageSize = 20,
+        [FromQuery] string? search = null, [FromQuery] bool sortDesc = true,
+        [FromQuery] BudgetPhase? phase = null,
+        [FromQuery] Guid? projectId = null,
+        [FromQuery] int? namNganSach = null,
+        CancellationToken ct = default)
+        => Ok(await mediator.Send(new ListBudgetsQuery(phase, projectId, namNganSach)
+        { Page = page, PageSize = pageSize, Search = search, SortDesc = sortDesc }, ct));
+
+    [HttpGet("{id:guid}")]
+    public async Task<ActionResult<BudgetDetailBundleDto>> Get(Guid id, CancellationToken ct)
+        => Ok(await mediator.Send(new GetBudgetQuery(id), ct));
+
+    [HttpPost]
+    public async Task<ActionResult<object>> Create([FromBody] CreateBudgetCommand cmd, CancellationToken ct)
+    {
+        var id = await mediator.Send(cmd, ct);
+        return CreatedAtAction(nameof(Get), new { id }, new { id });
+    }
+
+    [HttpPut("{id:guid}")]
+    public async Task<IActionResult> Update(Guid id, [FromBody] UpdateBudgetDraftCommand cmd, CancellationToken ct)
+    {
+        if (id != cmd.Id) return BadRequest(new { detail = "ID không khớp" });
+        await mediator.Send(cmd, ct);
+        return NoContent();
+    }
+
+    [HttpPost("{id:guid}/transitions")]
+    public async Task<IActionResult> Transition(Guid id, [FromBody] TransitionBudgetBody body, CancellationToken ct)
+    {
+        await mediator.Send(new TransitionBudgetCommand(id, body.TargetPhase, body.Decision, body.Comment), ct);
+        return NoContent();
+    }
+
+    [HttpDelete("{id:guid}")]
+    public async Task<IActionResult> Delete(Guid id, CancellationToken ct)
+    {
+        await mediator.Send(new DeleteBudgetCommand(id), ct);
+        return NoContent();
+    }
+
+    [HttpPost("{id:guid}/details")]
+    public async Task<ActionResult<object>> AddDetail(Guid id, [FromBody] BudgetDetailBody body, CancellationToken ct)
+    {
+        var newId = await mediator.Send(new AddBudgetDetailCommand(
+            id, body.GroupCode, body.GroupName, body.ItemCode, body.NoiDung, body.DonViTinh,
+            body.KhoiLuong, body.DonGia, body.ThanhTien, body.GhiChu), ct);
+        return Ok(new { id = newId });
+    }
+
+    [HttpPut("{id:guid}/details/{detailId:guid}")]
+    public async Task<IActionResult> UpdateDetail(Guid id, Guid detailId, [FromBody] BudgetDetailBody body, CancellationToken ct)
+    {
+        await mediator.Send(new UpdateBudgetDetailCommand(
+            id, detailId, body.GroupCode, body.GroupName, body.ItemCode, body.NoiDung, body.DonViTinh,
+            body.KhoiLuong, body.DonGia, body.ThanhTien, body.GhiChu), ct);
+        return NoContent();
+    }
+
+    [HttpDelete("{id:guid}/details/{detailId:guid}")]
+    public async Task<IActionResult> DeleteDetail(Guid id, Guid detailId, CancellationToken ct)
+    {
+        await mediator.Send(new DeleteBudgetDetailCommand(id, detailId), ct);
+        return NoContent();
+    }
+
+    [HttpGet("{id:guid}/changelogs")]
+    public async Task<List<BudgetChangelogDto>> GetChangelogs(Guid id, CancellationToken ct)
+        => await mediator.Send(new ListBudgetChangelogsQuery(id), ct);
+}
+
+public record TransitionBudgetBody(BudgetPhase TargetPhase, ApprovalDecision Decision, string? Comment);
+public record BudgetDetailBody(
+    string GroupCode, string GroupName, string? ItemCode, string NoiDung,
+    string? DonViTinh, decimal KhoiLuong, decimal DonGia, decimal ThanhTien, string? GhiChu);