docs(env): refresh ENVIRONMENT.md — document all 34 drifted env vars

[woolcoxm]

What

docs/ENVIRONMENT.md claims to be "generated from source by scanning every getenv() site" — but it had drifted far behind the code. Running the exact reconciliation procedure documented in MAINTAINING-DOCS.md, I found 34 engine env vars read by the code but undocumented, and nothing stale to remove.

# in code, NOT documented  ->  34 vars (before this PR)
comm -23 <(git grep -hoE 'getenv\("[A-Za-z0-9_]+"\)' -- 'c/*.c' 'c/*.cu' 'c/*.mm' | sed 's/getenv("\([^"]*\)")/\1/' | sort -u) \
         <(perl -ne 'while(/`([A-Z][A-Z0-9_]{1,})`/g){print "$1\n"}' docs/ENVIRONMENT.md | sort -u)

What changed

Added all 34 vars to the correct sections. Defaults and effects are taken from the source (the ternary default + inline comment at each call site), per the maintenance rules — nothing invented.

Performance / tuning (11):
COLI_NUMA, PILOT_TWO, COUPLE / COUPLE_K / COUPLE_D, ROUTE_TRACE, COLI_NO_FUSED_PAIR, DISK_SPLIT, I4S, SPEC_PIN, COLI_RAM_OVERCOMMIT

CUDA (16):
COLI_CUDA_ATTN_SHARD, COLI_CUDA_PIPE / _PIPE_SHARD / _PIPE_S_MIN, COLI_CUDA_MTP, COLI_CUDA_ASYNC, COLI_CUDA_DUAL_PROJ, COLI_CUDA_W4_PACKED, COLI_CUDA_TC_INT4 / _TC_MIN_ROWS / _TC_W4A16 / _TC_W4A16_MIN, COLI_CUDA_SHARED_W4A16 / _SHARED_W4A16_MIN_ROWS, COLI_METAL_UNTRACKED

Advanced / debug (7):
SCHEMA, EXPERT_BUDGET / EXPERT_BUDGET_EXPERIMENTAL (noting the #303 quarantine), TOKENS, SCORE_PREFIX, REPIN_VERBOSE, PPL (olmoe-only), COLI_PROMPT (in the CLI section)

Also bumped the "Generated from" line to dev @ d5327e2 and noted the scan now covers olmoe.c, backend_cuda.cu, backend_metal.mm (not just glm.c).

Verification

The code-vs-doc diff is now empty — all 111 distinct C env vars are documented:

comm -23 code_vars.txt doc_vars.txt   # (empty)

The reverse diff (doc vars not in C code) is 14 entries, all legitimate: 11 Python-side vars (COLI_API_KEY, COLI_DEBUG, …) correctly placed in the "Server / CLI" section (they're read by coli / openai_server.py, not the C engine), plus 3 prose constants named inside descriptions (IOSQE_ASYNC, O_DIRECT, and the VAR format placeholder).

Docs-only change; no build/test impact.