feat(backend): add knowledge base, innovation library and trends modules

Add knowledge item and innovation CRUD with search/filtering, published-only visibility for non-staff, admin publish/update, challenge dictionary, problem aggregation with trends (admin only) and canonical embedding text preparation for matchmaking.

backend/Controllers/InnovationsController.cs

@@ -0,0 +1,91 @@
+using Asp.Versioning;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using TarninaHub.Application.Abstractions;
+using TarninaHub.Application.Dtos;
+using TarninaHub.Application.Mappings;
+using TarninaHub.Application.Security;
+
+namespace TarninaHub.Controllers;
+
+[ApiController]
+[ApiVersion("1.0")]
+[Route("api/innovations")]
+[Authorize]
+public class InnovationsController : ControllerBase
+{
+    private readonly IInnovationService _innovations;
+
+    public InnovationsController(IInnovationService innovations)
+    {
+        _innovations = innovations;
+    }
+
+    [HttpGet]
+    public async Task<ActionResult<IReadOnlyList<InnovationResponse>>> List(
+        [FromQuery] string? challengeId,
+        [FromQuery] string? stage,
+        [FromQuery] string? q,
+        CancellationToken cancellationToken)
+    {
+        var innovations = await _innovations.ListAsync(challengeId, stage, q, !IsStaff(), cancellationToken);
+
+        return Ok(innovations);
+    }
+
+    [HttpGet("{innovationId}")]
+    public async Task<ActionResult<InnovationResponse>> GetById(
+        string innovationId,
+        CancellationToken cancellationToken)
+    {
+        var innovation = await _innovations.GetAsync(innovationId, cancellationToken);
+
+        return innovation is null ? NotFound() : Ok(innovation);
+    }
+
+    [HttpPost]
+    [Authorize(Policy = Policies.OperatorOrAdmin)]
+    public async Task<ActionResult<InnovationResponse>> Create(
+        InnovationRequest request,
+        CancellationToken cancellationToken)
+    {
+        if (!ValidateStage(request.Stage))
+        {
+            return InvalidStage();
+        }
+
+        var created = await _innovations.CreateAsync(request, cancellationToken);
+
+        return CreatedAtAction(nameof(GetById), new { innovationId = created.Id }, created);
+    }
+
+    [HttpPut("{innovationId}")]
+    [Authorize(Policy = Policies.OperatorOrAdmin)]
+    public async Task<ActionResult<InnovationResponse>> Update(
+        string innovationId,
+        InnovationRequest request,
+        CancellationToken cancellationToken)
+    {
+        if (!ValidateStage(request.Stage))
+        {
+            return InvalidStage();
+        }
+
+        var updated = await _innovations.UpdateAsync(innovationId, request, cancellationToken);
+
+        return updated is null ? NotFound() : Ok(updated);
+    }
+
+    private bool ValidateStage(string? stage) => InnovationStageWire.IsValid(stage);
+
+    private ActionResult InvalidStage()
+    {
+        ModelState.AddModelError(nameof(InnovationRequest.Stage),
+            "Stage must be one of: idea, pilot, scaling, service.");
+
+        return ValidationProblem(ModelState);
+    }
+
+    private bool IsStaff() =>
+        User.IsInRole(RoleNames.Operator) || User.IsInRole(RoleNames.Manager) || User.IsInRole(RoleNames.Admin);
+}