reference/: vendor kernel drivers as git submodules

[josephnef]

What

Replaces the 1.2 GB of gitignored full clones under reference/ with pinned git submodules, so contributors share the same fork+commit ground-truth without committing driver source into devourer's history — the parent repo gains only gitlinks (+29 lines total).

Fork choices (one dir per driver)

submodule	tracks	why
rtl8812au, rtl88x2bu, rtl88x2cu, rtl88x2eu	josephnef/* forks of OpenHD @ devourer-kbuild	OpenHD is the FPV/wifibroadcast lineage matching devourer (runtime TX-power-index + raw injection) — vs aircrack-ng (pentest) / morrownr (managed-AP, no injection)
8821cu	morrownr/8821cu-20210916 @ main	canonical monitor-capable 8821CU; builds clean
rtl88x2eu-5mhz	libc0607/rtl88x2eu-20230815 @ 5mhz_bw	not a duplicate — the only fork with the working R_0x9b4 5 MHz DAC-divider, the Jaguar3 narrowband ground-truth for tests/jaguar3_eu_kernel_5mhz_sdr.sh + jaguar3_eu_5mhz_mirror_ab.sh. OpenHD's lineage dropped this branch, so both are tracked. (was rtl88x2eu-2023-5mhz)

Build patches preserved

The four OpenHD drivers need small kernel-6.x kbuild-compat patches (EXTRA_CFLAGS→ccflags-y, from_timer→timer_container_of) to build their .ko on modern host/VM kernels. These live as one patch commit on each devourer-kbuild branch (= pinned upstream commit + patch), so everyone builds the reference .ko identically.

Housekeeping

• Chip-id / kernel-bind helpers moved reference/ → tests/ (chipid_probe.c, read_8821c_chipid.sh, 8821cu_hwtest.sh); committed compiled probe binary dropped. read_8821c_chipid.sh builds into a tempdir; 8821cu_hwtest.sh resolves the .ko via the submodule path.
• Rationale + git submodule update --init --recursive documented in reference/README.md, pointer added to CLAUDE.md.

Verification

• Each reference/* is a mode-160000 gitlink — zero driver source in devourer history.
• tools/extract_*.py reproduce hal/ byte-for-byte from the submodule checkouts (fork content = ground-truth).
• Moved scripts pass bash -n; chipid_probe.c compiles; build clean; 15/15 ctest pass.
• Local reference/ 1.2 G → 272 M (shallow); smaller for fresh consumer inits.

Note for reviewers

The devourer-kbuild/5mhz_bw submodule branches are non-default, so init needs --recursive (branches are recorded in .gitmodules). Fetch with:

git submodule update --init --recursive

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