fix: add fallback resolution and diagnostics to build_context

When build_context performs an exact permalink lookup that returns 0
results, it now tries three fallback resolution strategies before
giving up — mirroring the multi-strategy approach already used by
read_note:

1. Wildcard prefix match (*/path): recovers notes when stored permalinks
   carry an extra leading segment (e.g. project prefix) not present in
   the caller's identifier.
2. Strip-prefix exact lookup: recovers notes when the caller included an
   extra leading segment absent from stored permalinks.
3. Title FTS search on the last path segment: recovers notes when
   permalink normalization diverges from stored values.

Diagnostic fields added:
- ContextMetadata.resolved_path: the normalized path that was tried
- ContextMetadata.no_primary_match: machine-readable reason when all
  fallbacks are exhausted, allowing clients to distinguish "lookup miss"
  from "note has no relations"

Both fields are surfaced through MemoryMetadata (schema) and
to_graph_context (API utils) so they appear in the JSON response.

Backward compatibility: successful exact lookups are unchanged. The
fallbacks are only entered when the primary search returns 0 rows.

Closes #582

Co-authored-by: Paul Hernandez <phernandez@users.noreply.github.com>
Signed-off-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

src/basic_memory/api/v2/utils.py

@@ -138,6 +138,8 @@ async def to_graph_context(
         total_results=context_result.metadata.primary_count + context_result.metadata.related_count,
         total_relations=context_result.metadata.total_relations,
         total_observations=context_result.metadata.total_observations,
+        resolved_path=context_result.metadata.resolved_path,
+        no_primary_match=context_result.metadata.no_primary_match,
     )
 
     # Return new GraphContext with just hierarchical results