Surface §5 geometry operators to compiled El

Register the six engram_geo_*_json operators in the compiler builtin_arity
table (bare heavy-runtime names + __ seed names, mirroring engram_activate_json)
and add the engram.el module wrappers, so a compiled El (CGI) program can call
them by name. The heavy-runtime C functions already existed (el_runtime.c:12287+,
declared el_runtime.h:627-632); this completes the EL call surface.

The shipped elc already emits a direct C call for these builtins (unknown
ident-calls pass through), so no self-host compiler fold — the memory-heavy,
drift-prone step — was required. Demonstrated end-to-end: a compiled geo_ops_demo.el
booted a copy of the store (13,036 nodes) and produced real subtract/distance JSON
on two real neighborhoods; test_geo_ops.c stays 20/20, ASan/UBSan clean.

Also brace the centroid_unit normalization if/else in engram_geometry.c to clear
the misleading-indentation warning (behavior-neutral).

lang/runtime/engram_geometry.c

@@ -1415,7 +1415,8 @@ int engram_geo_reify_index_finalize(GeoReifyIndex* ix){
             r->centroid_unit=malloc((size_t)r->dim*sizeof(float));
             if(r->centroid_unit){
                 double nrm=0; for(int d=0;d<r->dim;d++){ double v=(double)r->centroid_raw[d]-ix->mean[d]; r->centroid_unit[d]=(float)v; nrm+=v*v; }
-                nrm=sqrt(nrm); if(nrm>1e-12) for(int d=0;d<r->dim;d++) r->centroid_unit[d]=(float)(r->centroid_unit[d]/nrm);
+                nrm=sqrt(nrm);
+                if(nrm>1e-12){ for(int d=0;d<r->dim;d++) r->centroid_unit[d]=(float)(r->centroid_unit[d]/nrm); }
                 else { free(r->centroid_unit); r->centroid_unit=NULL; }
             }
         }