v0.7.2: self-help (/why) + CONFIG injection — TDD

- CONFIG section in system prompt: providers, context window, gate count,
  rules learned, docs path
- /why TUI command: shows most recent gate trace from message history
- assemble-config-section reads live state at each think() call
- Core: 75/76  TUI Main: 77/78 (1 pre-existing RCE test flake)

lisp/core-reason.lisp

@@ -88,7 +88,7 @@
                             (symbol-value '*provider-cascade*)))))
     (when (boundp '*hitl-pending*)
       (setf rules-count (hash-table-count (symbol-value '*hitl-pending*))))
-    (format nil "CONFIG: You are Passepartout v0.7.2. Provider: ~a. Context: ~d tokens. Security gates: ~d active. Rules learned: ~d."
+    (format nil "CONFIG: You are Passepartout v0.7.2. Provider: ~a. Context: ~d tokens. Security gates: ~d active. Rules learned: ~d. Documentation: ~/memex/projects/passepartout/docs/USER_MANUAL.org."
             (if (string= provider-names "") "default" provider-names)
             context-window gate-count rules-count)))