docs: refresh architecture map

[Daniiiil1]

What changed

• add the target-agnostic USART driver layer to the repository map
• document the current firmware services, including I2C, MCTP, SPDM, firmware management, and the orchestrator
• add AST10x0 and mock targets alongside Earl Grey and VeeR
• explain how interfaces, platform implementations, target backends, firmware images, and host/target tests are separated

Why

The architecture guide no longer reflected several directories and abstractions that are present on main. Updating the map makes it easier for new contributors to find the correct layer for portable protocol logic, silicon-specific implementations, and system-image tests.

Validation

• git diff --check
• npx --yes @bazel/bazelisk build //docs was attempted twice. The first run timed out fetching Pigweed LLVM through CIPD. The second completed analysis and 705/706 actions, then failed while linking the external mdBook tool because Pigweed’s macOS sysroot could not resolve the CFNetwork framework re-export from CoreServices. The failure occurs in the external documentation toolchain before processing this Markdown change.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Daniiiil1 / name: Daniil Mordanov (943ac55)

[rusty1968]

we have renamed fwmanager to orchestrator.

[rusty1968]

the refresh needs a refresher.