refactor(core): extract path_resolver module, fix old_path matching in who

Extract shared path resolution logic from who.rs into a new
core::path_resolver module for cross-module reuse. Functions moved:
escape_like, normalize_repo_path, PathQuery, SuffixResult,
build_path_query, suffix_probe. Duplicate escape_like copies removed
from list.rs, project.rs, and filters.rs — all now import from
path_resolver.

Additionally fixes two bugs in query_expert_details() and
query_overlap() where only position_new_path was checked (missing
old_path matches for renamed files) and state filter excluded 'closed'
MRs despite the main scoring query including them with a decay
multiplier.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/search/filters.rs

@@ -1,4 +1,5 @@
 use crate::core::error::Result;
+use crate::core::path_resolver::escape_like;
 use crate::documents::SourceType;
 use rusqlite::Connection;
 
@@ -43,12 +44,6 @@ impl SearchFilters {
     }
 }
 
-fn escape_like(s: &str) -> String {
-    s.replace('\\', "\\\\")
-        .replace('%', "\\%")
-        .replace('_', "\\_")
-}
-
 pub fn apply_filters(
     conn: &Connection,
     document_ids: &[i64],