cfw: dsc: Add FORCE_DSC_MAXSLIDE opt-in to zero maxSlide on non-27 bases

patch-dsc-maxslide self-gates to a no-op when the shared cache fits the
vphone600 26.x kernel's 6 GiB region, which 26.x/18.x bases always do, so
it only fires on 27. Add a --force flag that bypasses the fits-check and
zeroes maxSlide unconditionally (still idempotent), and a
FORCE_DSC_MAXSLIDE=1 env opt-in in cfw_install.sh that runs it on non-27
bases. Default off; 27 behavior unchanged.

Also fix the installer env-threading in cfw_install_host.sh: a
${VAR:+NAME=val} word produced by expansion is not parsed as a shell
assignment (zsh runs it as a command), so route the assignments through
env. This makes FORCE_DSC_MAXSLIDE reach the installer and repairs the
same latent bug for SPOOF_BUILD.

Verified on a 26.4 JB VM: FORCE_DSC_MAXSLIDE=1 yields on-disk maxSlide=0
and a live shared-cache slide of 0x0 (dyld maps the cache at its
preferred base 0x180000000 in rpcserver_ios), versus the nonzero slide a
stock 26.4 boot picks.

Docs + research/0_binary_patch_comparison.md updated (README and the ja/ko/zh
translations).

Co-Authored-By: Claude Fable 5 <[email protected]>

docs/README_ja.md

@@ -190,6 +190,7 @@ make cfw_install
 # または: make cfw_install_jb        # 脱獄バリアント
 # または: make cfw_install_exp       # 実験バリアント（脱獄 + リサーチパッチスタック）
 # または: SPOOF_BUILD=23F77 make cfw_install_exp   # ProductBuildVersion も書き換え
+# または: FORCE_DSC_MAXSLIDE=1 make cfw_install    # 27 以外のベースで DSC maxSlide=0 を強制（全バリアント対応、27 は自動）
 ```
 
 ## 初回起動

docs/README_ko.md

@@ -190,6 +190,7 @@ make cfw_install
 # 또는: make cfw_install_jb        # 탈옥 변형
 # 또는: make cfw_install_exp       # 실험 변형 (탈옥 + 연구 패치 스택)
 # 또는: SPOOF_BUILD=23F77 make cfw_install_exp   # 추가로 ProductBuildVersion 재작성
+# 또는: FORCE_DSC_MAXSLIDE=1 make cfw_install    # 27 이외 베이스에서 DSC maxSlide=0 강제 (모든 변형, 27은 자동)
 ```
 
 ## 첫 부팅

docs/README_zh.md

@@ -190,6 +190,7 @@ make cfw_install
 # 或：make cfw_install_jb        # 越狱变体
 # 或：make cfw_install_exp       # 实验变体（越狱 + 研究补丁栈）
 # 或：SPOOF_BUILD=23F77 make cfw_install_exp   # 同时改写 ProductBuildVersion
+# 或：FORCE_DSC_MAXSLIDE=1 make cfw_install    # 在非 27 基础版本上强制 DSC maxSlide=0（所有变体；27 会自动执行）
 ```
 
 ## 首次启动