Implement CE-WP-0009: wire umbrella to @citation-evidence/engine

Add link: dependency on citation-engine, retarget @shared/@engine aliases,
remove in-repo shared/engine copies. ADR-0002 accepted (option B).
172 tests, typecheck, and lint pass.

tsconfig.json

@@ -25,8 +25,8 @@
 
     "baseUrl": ".",
     "paths": {
-      "@shared/*": ["src/shared/*"],
-      "@engine/*": ["src/engine/*"],
+      "@shared/*": ["../citation-engine/src/shared/*"],
+      "@engine/*": ["../citation-engine/src/engine/*"],
       "@anchor/*": ["src/anchor/*"],
       "@source/*": ["src/source/*"],
       "@work/*":   ["src/work/*"],