Add JB install pipeline and update docs

Add jailbreak extension patchers and targets:
- kernel_jb.py: 22 dynamic kernel patches (trustcache, execve cs_flags,
  sandbox ops, task/VM, kcall10 syscall hook, ~160 total modifications)
- txm_jb.py: 13 TXM patches (CS validation, get-task-allow, debugger
  entitlement, dev mode bypass)
- iboot_jb.py: iBSS nonce generation skip
- cfw.py: launchd jetsam patch, dylib injection commands
- fw_patch_jb.py: orchestrator running base + JB extension patches
- cfw_install_jb.sh: JB install phases (launchd jetsam fix, procursus
  bootstrap + Sileo deployment)

3 kernel patches still WIP (nvram_verify_permission, thid_should_crash,
hook_cred_label_update_execve) — strategies documented in
researchs/kernel_jb_remaining_patches.md.

All base (non-JB) code paths verified unaffected — kernel.py produces
identical 25 patches, cfw.py base commands unchanged.

Add Linux venv setup script; tweak Makefile help

Add scripts/setup_venv_linux.sh to create a Python virtualenv on Debian/Ubuntu (or dnf-based) systems, install system packages and Python requirements, and verify core imports (capstone, keystone, pyimg4). Also update Makefile help text to mark the fw_patch_jb target as WIP. This simplifies local development setup on Linux and clarifies that the JB extension patches are a work in progress.

Update AGENTS.md: mark cfw_install_jb.sh as complete

Makefile

@@ -45,6 +45,7 @@ help:
 	@echo "Firmware pipeline:"
 	@echo "  make fw_prepare              Download IPSWs, extract, merge"
 	@echo "  make fw_patch                Patch boot chain (6 components)"
+	@echo "  make fw_patch_jb             Run fw_patch + JB extension patches (WIP)"
 	@echo ""
 	@echo "Restore:"
 	@echo "  make restore_get_shsh        Fetch SHSH blob from device"
@@ -56,6 +57,7 @@ help:
 	@echo ""
 	@echo "CFW:"
 	@echo "  make cfw_install             Install CFW mods via SSH"
+	@echo "  make cfw_install_jb          Install CFW + JB extensions (jetsam/procursus/basebin)"
 	@echo ""
 	@echo "Variables: VM_DIR=$(VM_DIR) CPU=$(CPU) MEMORY=$(MEMORY) DISK_SIZE=$(DISK_SIZE)"
 
@@ -130,7 +132,7 @@ boot_dfu: build
 # Firmware pipeline
 # ═══════════════════════════════════════════════════════════════════
 
-.PHONY: fw_prepare fw_patch
+.PHONY: fw_prepare fw_patch fw_patch_jb
 
 fw_prepare:
 	cd $(VM_DIR) && bash "$(CURDIR)/$(SCRIPTS)/fw_prepare.sh"
@@ -138,6 +140,9 @@ fw_prepare:
 fw_patch:
 	cd $(VM_DIR) && $(PYTHON) "$(CURDIR)/$(SCRIPTS)/fw_patch.py" .
 
+fw_patch_jb:
+	cd $(VM_DIR) && $(PYTHON) "$(CURDIR)/$(SCRIPTS)/fw_patch_jb.py" .
+
 # ═══════════════════════════════════════════════════════════════════
 # Restore
 # ═══════════════════════════════════════════════════════════════════
@@ -166,7 +171,10 @@ ramdisk_send:
 # CFW
 # ═══════════════════════════════════════════════════════════════════
 
-.PHONY: cfw_install
+.PHONY: cfw_install cfw_install_jb
 
 cfw_install:
 	cd $(VM_DIR) && zsh "$(CURDIR)/$(SCRIPTS)/cfw_install.sh" .
+
+cfw_install_jb:
+	cd $(VM_DIR) && zsh "$(CURDIR)/$(SCRIPTS)/cfw_install_jb.sh" .