refactor: move firmware workspace under firmware

firmware/README.md

@@ -0,0 +1,26 @@
+# Firmware
+
+This directory is the Kaptan flight-controller firmware workspace. It owns the
+Rust workspace manifest, board declarations, platform implementation, reusable
+firmware crates, simulator, firmware scripts, and firmware test fixtures.
+
+```text
+firmware/
+├── boards/     immutable board declarations and linker layouts
+├── libs/       reusable no_std firmware crates
+├── platforms/  hardware platform composition
+├── tools/      SITL and firmware development tooling
+├── scripts/    packaging, analysis, and coverage helpers
+└── tests/      firmware integration-test fixtures
+```
+
+Run Cargo commands from this directory:
+
+```sh
+cd firmware
+cargo test --workspace --locked --offline
+```
+
+The sibling `ground-suite/` directory is the desktop ground-control
+application. It is intentionally a separate project and does not participate
+in the firmware Cargo workspace.