feat(ugc): answer the client's UGC manifest requests without 3D services

With UGCUSE3DSERVICES=7:0 (the client's default) the client asks its world for
a blueprint file's MD5 and size (REQUEST_UGC_MANIFEST_INFO, world 27) and then
downloads BrickModels/UserMade/<id % 1000>/<id>.<ext>.sd0. Layouts checked in
the 1.10.64 client: the request is a u64 blueprint id and a u8 resource type;
the answer (UGC_MANIFEST_RESPONSE, client 60) repeats them and adds a u8 valid,
the u32 size and the 16 byte MD5 of the inflated file, 37 bytes after the 0x53
exactly or the client drops it.

- dNet: WorldPackets::RequestUgcManifestInfo, ClientPackets::UgcManifestResponse
  (eUgcResourceType), with byte tests against the client's layouts.
- Database: ugc_file_checksums (per model or module combination and file) and
  ugc_modular_build.combination_id (migrations 89 / 72), GetUgcFileChecksum
  looks a blueprint up as a model, else as a build through its combination.
- UGC server: every download is also written as .sd0 (Sd0::Compress); workers
  hand the checksums back and the main thread stores them; old items get their
  sd0 icon and checksum, and builds their combination id, once at start-up, a
  few per tick; serves <dir>/BrickModels/UserMade/<bucket>/<id>.<ext>.sd0 under
  client_path, /<folder>/UserBrickModels and the root (.hkx 404).
- World: UgcManifest answers on the main thread with one indexed query per
  request; files not made yet are answered when they are (looked at again
  every 5 seconds), and a model in its quiet period is made right away. No
  worker threads, HTTP or file reads in the world.

Off by default (ugc_manifest=0): checked in game, the client then downloads
from http://127.0.0.1:80/lwoclient/UserBrickModels/ whatever its boot.cfg says
and logs the player out when it can't connect, so icons need the UGC server on
port 80 of each player's machine. docs/UgcServer.md has the details.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dDatabase/GameDatabase/ITables/IUgc.h

@@ -107,5 +107,26 @@ public:
 
 	// How many models are in each state
 	virtual std::vector<std::pair<eProcessState, uint64_t>> GetUgcProcessCounts() = 0;
+
+	// ---- Checksums of the files the UGC server made (ugc_file_checksums), for the client's manifest requests ----
+
+	// What the files are stored under: a player model's ugc id, or a combination of car or rocket modules
+	enum class eFileOwner : int32_t {
+		MODEL = 0,
+		COMBINATION = 1
+	};
+
+	// A made file as the client has it after inflating the download: its MD5 (32 lowercase hex digits) and size
+	struct FileChecksum {
+		std::string md5;
+		uint32_t size{};
+	};
+
+	// Records (or replaces) the checksum of a made file, e.g. "icon.dds" or "model.nif"
+	virtual void SetUgcFileChecksum(const eFileOwner owner, const LWOOBJID storageId, const std::string_view file, const std::string_view md5, const uint32_t size) = 0;
+
+	// The checksum of a blueprint's file: a player model's (the blueprint is its ugc id), else a car or rocket build's
+	// (the blueprint is its ugc_modular_build id; the file is its combination's)
+	virtual std::optional<FileChecksum> GetUgcFileChecksum(const LWOOBJID blueprintId, const std::string_view file) = 0;
 };
 #endif  //!__IUGC__H__

dDatabase/GameDatabase/ITables/IUgcModularBuild.h

@@ -29,6 +29,12 @@ public:
 	virtual std::vector<IUgc::ProcessInfo> GetModularBuildProcessList(const std::optional<IUgc::eProcessState> state, const std::string_view search, const uint32_t offset, const uint32_t limit) = 0;
 	virtual std::vector<std::pair<IUgc::eProcessState, uint64_t>> GetModularBuildProcessCounts() = 0;
 
+	// The combination of modules a build was made as (UgcModularKey::StorageId of its modules), whose files it shares
+	virtual void SetModularBuildCombination(const LWOOBJID id, const LWOOBJID combinationId) = 0;
+
+	// Up to `limit` builds whose combination isn't recorded yet (combination_id 0): their ids and modules
+	virtual std::vector<PendingBuild> GetModularBuildsWithoutCombination(const uint32_t limit) = 0;
+
 	// How many builds there are of each ldf_config as stored (the same modules may be written differently)
 	virtual std::vector<std::pair<std::string, uint64_t>> GetModularBuildConfigCounts() = 0;