The reranker document text now reflects the traversal direction,
showing only the new information relative to the frontier entity:
- From S (subject is frontier): text = "{predicate} {object}"
- From O (object is frontier): text = "{subject} {predicate}"
- From P (predicate is frontier): text = "{subject} {object}"

This eliminates duplicate reranker texts when traversing inward
from shared object nodes (e.g. 18 CPUs all producing identical
"hasSubcategory Processors" text when the subject was dropped).

execute_batch_triple_queries now returns (triple, direction)
tuples so hop_and_filter can select the appropriate text format.

Updates tech spec to document the direction-aware approach.
Adds unit tests for direction tracking and reranker text
construction.