Upgrade Knip back to 6, with raw transfer disabled

Knip 5 is effectively frozen: 5.88.1 (2026-03-19) was its last release,
with only three patches after 6.0.0 shipped and none since.

The reason for the earlier downgrade (968cc72) was misdiagnosed. The 6 GiB
allocation is not the Rust-side arena tracked in oxc-project/oxc#20513, but
a JS-side `new ArrayBuffer(BLOCK_SIZE + BLOCK_ALIGN)` in oxc-parser's
raw-transfer path, allocated by V8. Linux refuses it under heuristic
overcommit on the CI runner (3.7 GB RAM, no swap). The upstream allocator
work that has landed does not touch this path, so waiting on it would not
have helped.

Set KNIP_DISABLE_RAW_TRANSFER=1 in the `knip` script instead, and route
lefthook and `check` through the script rather than the bare binary — the
default path would otherwise crash with an opaque RangeError. Raw transfer
is worth ~5% on a repo this size (3.1s vs 3.15s); the upstream 2-4x figure
applies to large codebases. Knip 6 is still ~20% faster than 5 overall.

No change in unused-code detection. Verified under overcommit_memory=0 on
Linux as well as locally.

Closes #11

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

knip.json

@@ -1,5 +1,5 @@
 {
-	"$schema": "https://unpkg.com/knip@5/schema.json",
+	"$schema": "https://unpkg.com/knip@6/schema.json",
 	"workspaces": {
 		".": {
 			"entry": ["scripts/*.mjs"]