docs(agents): document the Unreal Engine and C++ skill packs

AGENTS.md only described the Blender packs. Add the two skill sets that shipped
with the project since:

- 31 Unreal Engine packs (MIT, quodsoler/unreal-engine-skills f3742d7) at
  .agents/skills/ue-*/, targeting UE 5.8 C++, with ue-project-context as the entry
  point and a discipline mapping to this project's work.
- The cpp router (MIT, DiamonDinoia/skill-cpp f2617fb) at .agents/skills/cpp/, for
  general C++11-23 against the Core Guidelines; the project is C++20.

AGENTS.md

@@ -197,6 +197,33 @@ Do not copy the common packs into the repository: a second copy under a differen
 
 **Caveat:** the skill packs assume MCP-driven interactive Blender. This project runs Blender headless via scripts in `Tools/` — use the skills as method guides (checklists, naming conventions, proportions, validation steps), not for their MCP tooling. The headless scripts remain the execution path.
 
+## Unreal Engine skills
+
+The 31 Unreal Engine skill packs (MIT, [quodsoler/unreal-engine-skills](https://github.com/quodsoler/unreal-engine-skills) `f3742d7`) live in the repository at `.agents/skills/ue-*/` and target **UE 5.8 C++**. Each carries API examples verified against the 5.8 headers plus a deprecated-API table that maps old calls to the 5.8 forms. They are agent instructions, not add-ons.
+
+`.agents/skills/ue-project-context/` is the entry point: it writes `.agents/ue-project-context.md` (module names, conventions, enabled plugins), and every other UE skill reads that file first. Refresh it when the project changes — new module, new plugin, engine bump — before consulting the rest.
+
+The general mapping to this project's work:
+
+- **Build and modules** — `ue-module-build-system` (Build.cs, unresolved externals, include order, plugin enablement).
+- **Reflection and core types** — `ue-cpp-foundations` (UCLASS/UPROPERTY/UFUNCTION, TObjectPtr, delegates), `ue-blueprint-cpp-interop`.
+- **Actor/component lifecycle** — `ue-actor-component-architecture` (spawning, attachment, tick groups, EndPlay).
+- **Player and pawns** — `ue-character-movement` (the character's walking), `ue-gameplay-framework` (GameMode/Pawn/Controller), `ue-input-system` (Enhanced Input). The Chaos vehicle is the `ChaosVehiclesPlugin` — see the vehicle notes in `TODO.md`, not a skill pack.
+- **Physics and collision** — `ue-physics-collision` (channels, traces, overlaps, profiles).
+- **Materials and rendering** — `ue-materials-rendering`, `ue-niagara-effects`.
+- **World and streaming** — `ue-world-level-streaming` (World Partition, level streaming, travel), `ue-procedural-generation` (PCG).
+- **Data, save and serialization** — `ue-data-assets-tables`, `ue-serialization-savegames`.
+- **Networking** — `ue-networking-replication` (replication, RPCs, relevance).
+- **UI** — `ue-ui-umg-slate` (UMG, Slate, Common UI).
+- **Debugging, profiling, tests** — `ue-testing-debugging`, `ue-async-threading`.
+- **Editor tooling** — `ue-editor-tools` (detail customizations, menus, factories).
+- **Animation** — `ue-animation-system` (AnimInstance, montages, notifies, root motion).
+- **As-needed** — `ue-ai-navigation`, `ue-audio-system`, `ue-game-features`, `ue-gameplay-abilities` (GAS), `ue-gameplay-cameras`, `ue-gameplay-tags-messaging`, `ue-mass-entity`, `ue-mover`, `ue-sequencer-cinematics`, `ue-state-trees`.
+
+## C++ skill
+
+One router skill, `cpp` (MIT, [DiamonDinoia/skill-cpp](https://github.com/DiamonDinoia/skill-cpp) `f2617fb`), lives at `.agents/skills/cpp/` and covers general C++11 through C++23 against the C++ Core Guidelines. It detects the project language standard from the build system (**C++20** for this project, from the UBT compile flags), then loads the matching standard reference plus the topic references the task touches. Load it for any C++ work that is not Unreal-specific; the UE skills supersede it for engine API questions.
+
 ## Licensing & Distribution
 
 - Publish project-owned code under a chosen open-source license.