Add FPGA project workspace layout

Software/README.md

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+# Software/
+
+Software that runs on the CPU: bare-metal firmware, BIOS, and kernels.
+Built with the RISC-V GCC toolchain (`riscv64-unknown-elf-gcc`). The `march`
+string evolves with the implemented ISA — see `CLAUDE.md`.

Software/bios/README.md

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+# Software/bios/
+
+BIOS / monitor: an interactive ROM program that talks over UART to peek/poke
+memory, dump registers, and load programs into RAM. Includes the ELF loader.
+
+**Phases:** 9 (BIOS monitor), 10 (ELF loader over UART).

Software/fw/README.md

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+# Software/fw/
+
+Bare-metal firmware: `crt0.S`, linker script, and the first C programs that
+run on the CPU. Also where `riscv-tests` integration lives.
+
+**Phases:** 8 (GCC toolchain, first C program, `riscv-tests`).

Software/kernel/README.md

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+# Software/kernel/
+
+Kernels that run on the core. Starts as a tiny custom kernel for learning
+trap/scheduling/syscalls; later hosts the Linux device tree, OpenSBI, and
+mainline Linux build artifacts.
+
+**Phases:** 11 (tiny kernel), 19 (Linux boot contract), 20 (Linux).