[backend/akko-client] Try to implement GET v1/pleroma/emoji

Akkoma-FE is doing something horrible here, I do not think this is
fixable without changing the FE itself.

Iceshrimp.Backend/Controllers/Pleroma/EmojiController.cs

@@ -0,0 +1,34 @@
+using System.Net;
+using System.Net.Mime;
+using Iceshrimp.Backend.Controllers.Mastodon.Attributes;
+using Iceshrimp.Backend.Controllers.Pleroma.Schemas.Entities;
+using Iceshrimp.Backend.Controllers.Shared.Attributes;
+using Iceshrimp.Backend.Core.Database;
+using Microsoft.AspNetCore.Cors;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.RateLimiting;
+using Microsoft.EntityFrameworkCore;
+
+namespace Iceshrimp.Backend.Controllers.Pleroma;
+
+[MastodonApiController]
+[EnableCors("mastodon")]
+[EnableRateLimiting("sliding")]
+[Produces(MediaTypeNames.Application.Json)]
+public class EmojiController(DatabaseContext db) : ControllerBase
+{
+	[HttpGet("/api/v1/pleroma/emoji")]
+	[ProducesResults(HttpStatusCode.OK)]
+	public async Task<Dictionary<string, PleromaEmojiEntity>> GetCustomEmojis()
+	{
+		var emoji = await db.Emojis.Where(p => p.Host == null)
+			.Select(p => KeyValuePair.Create(p.Name, new PleromaEmojiEntity
+			{
+				ImageUrl = new Uri(p.PublicUrl).AbsolutePath, // TODO: akkoma-fe expects *relative paths* instead of absolute URLs... i genuinely think this is unfixable without forking the fe
+				Tags     = p.Category == null ? new string[0] : new string[] { p.Category }
+			}))
+			.ToArrayAsync();
+
+		return new Dictionary<string, PleromaEmojiEntity>(emoji);
+	}
+}

Iceshrimp.Backend/Controllers/Pleroma/Schemas/Entities/PleromaEmojiEntity.cs

@@ -0,0 +1,9 @@
+using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
+
+namespace Iceshrimp.Backend.Controllers.Pleroma.Schemas.Entities;
+
+public class PleromaEmojiEntity
+{
+	[J("image_url")] public required string   ImageUrl { get; set; }
+	[J("tags")]      public          string[] Tags     { get; set; } = [];
+}