build: dynamically tangle to INSTALL_DIR without copying .org files

- Updated all 150+ :tangle headers across harness/ and skills/ to use elisp (expand-file-name) to target INSTALL_DIR dynamically.
- Cleaned up environment/ directory depth by moving memory-image.lisp to state/.
- Moved test scripts to tests/ and deleted redundant chat scripts.

skills/org-skill-llm-gateway.org

@@ -19,7 +19,7 @@ The gateway utilizes a functional dispatch pattern. A single entry point, `execu
 * Phase D: Build (Implementation)
 
 ** Implementation
-#+begin_src lisp :tangle ./org-skill-llm-gateway.lisp
+#+begin_src lisp :tangle (expand-file-name "org-skill-llm-gateway.lisp" (concat (or (getenv "INSTALL_DIR") ".") "/skills"))
 
 (defun get-nested (alist &rest keys)
   "Recursively extracts nested values from an alist, handling both objects and arrays."