restructure: code+libs under src/, runtime resources under data/

Separate the two concerns the repo root was mixing:
- src/   — bs/, modules/, libs/ (code + vendored libs)
- data/  — fpga_registry.yaml, probes.yaml, bsdl_files/, bscan_proxies/,
           scripts/ (everything the tool reads at runtime, CWD-relative)
- doc/   — kept at the root

CMake: repoint DIR_MODULES/DIR_LIBS and add_subdirectory at src/; emit
the binary at the build/ root (build/bs) via CMAKE_RUNTIME_OUTPUT_DIRECTORY
instead of the nested build/src/bs/. The jtag_core ../../libs path still
resolves since modules and libs moved together.

Runtime default paths now point under data/ (fpga.c, probes.c, script.c
bsdl_files lookup, init.c config.script). Docs (README/tutorial/CLAUDE)
updated for the new layout, src/ module paths, and ./build/bs.

Validated on the IGLOO2/FlashPro: profiles, autoinit, and svf_play all
work run from the repo root.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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