docs: add architecture overview with Mermaid diagrams

Two diagrams in docs/dev/ARCHITECTURE.md: how the relinker and the NID-patched system libraries produce a native program, and the graphics path from command buffers through the shader recompiler to Vulkan. README only gains a link.

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

README.md

@@ -4,7 +4,7 @@ Tool for automatic executables porting to Linux and Windows.
 
 Includes a [relinker](core/relinker) that converts executable to the target system's native format and implementations of [system prx libraries](core/libs/prx) suitable for dynamic linking. No emulation or separate runtime process.
 
-[Usage](docs/user/USAGE.md), [Build instructions](docs/dev/BUILD.md), [Technical debt of the project](docs/dev/TechnicalDebt.md), [code style conventions](docs/dev/CONVENTIONS.md), [contributing](CONTRIBUTING.md)
+[Usage](docs/user/USAGE.md), [Build instructions](docs/dev/BUILD.md), [Architecture](docs/dev/ARCHITECTURE.md), [Technical debt of the project](docs/dev/TechnicalDebt.md), [code style conventions](docs/dev/CONVENTIONS.md), [contributing](CONTRIBUTING.md)
 
 ## Status
 

docs/dev/ARCHITECTURE.md

@@ -0,0 +1,69 @@
+# Architecture
+
+How a PS5 executable becomes a native Linux or Windows program. Nothing is emulated: the converted executable runs as a normal process and calls native implementations of the system libraries.
+
+## Overview
+
+```mermaid
+flowchart LR
+    subgraph input["PS5 game"]
+        elf["input.elf"]
+        mods["sce_module/*"]
+    end
+
+    subgraph relinker["relinker (core/relinker)"]
+        direction TB
+        intel["--to-intel:<br/>lower AMD-only instructions<br/>(codegen)"]
+        pipeline["RelinkerPipeline:<br/>read imports by NID,<br/>check syscalls, filter unused NIDs,<br/>build SysV dynamic section"]
+        guest["GuestModuleBuilder:<br/>convert bundled modules"]
+        patcher["LinuxElfPatcher / WindowsPePatcher"]
+        intel -.-> pipeline --> guest --> patcher
+    end
+
+    subgraph build["build (core/libs)"]
+        direction TB
+        prx["core/libs/prx/*<br/>shared libraries"]
+        nid["nid_patcher:<br/>rename exports to their NIDs"]
+        prx --> nid
+    end
+
+    subgraph out["Native program"]
+        app["app.elf / app.exe"]
+        app0["app0/sce_module/*"]
+        libs["libs/*.prx"]
+    end
+
+    elf --> intel
+    mods --> guest
+    patcher --> app
+    guest --> app0
+    nid --> libs
+    app -- "OS loader binds imports by NID" --> libs
+    app0 -- "OS loader binds imports by NID" --> libs
+```
+
+- [`core/relinker/main.cpp`](../../core/relinker/main.cpp) runs the steps in this order. `--to-intel` is optional, see [USAGE.md](../user/USAGE.md).
+- Each library in [`core/libs/prx`](../../core/libs/prx) builds as a shared library. After the build, `nid_patcher` ([`core/libs/nid`](../../core/libs/nid)) renames every export to its NID, computed from the function name. `APS5_EXPORT("<nid>", func)` sets the NID directly when the name is unknown.
+
+## Graphics
+
+```mermaid
+flowchart LR
+    game["Game:<br/>command buffers"] --> submit["libSceAgcDriver/Submit<br/>DCB / ACB"]
+    submit --> pm4["Execution/Pm4:<br/>state, draws,<br/>dispatches"]
+    pm4 -- "shader + state" --> cache{"Compiled variant<br/>in memory or<br/>on disk?"}
+    cache -- yes --> vk
+    cache -- no --> dec
+
+    subgraph recompiler["core/shader/recompiler"]
+        dec["RdnaDecoder"] --> cf["ControlFlow:<br/>graph + structurize"]
+        cf --> tr["Translation:<br/>RDNA to IR"]
+        tr --> opt["Optimization:<br/>SSA, resources,<br/>bindings"]
+        opt --> spv["SpirvBackend:<br/>emit SPIR-V"]
+    end
+
+    spv --> vk["libSceAgcDriver/Graphics:<br/>Vulkan pipeline"]
+```
+
+- [`Recompiler.cpp`](../../core/shader/recompiler/Recompiler.cpp) runs the stages in this order. With `ANYPS5_ENABLE_SPIRV_TOOLS`, the SPIR-V is also validated and optimized with SPIRV-Tools.
+- `ShaderRecompiler::Recompile` keeps compiled variants in memory, and `ShaderDiskCache` stores them on disk so later runs reuse them.