fix(search): down-weight the project name in ranking — completes #720 (#748)

The per-word path fix (#745) brought the backend to parity but not above:
the project name still gave the lexically-matching stack a residual dir
match + an FTS class-name match, so a backend query that included the
project name still ranked the frontend at/above the backend.

Derive the project name from go.mod module / package.json name / repo dir,
and treat a query word matching it as non-discriminative: drop it from path
relevance and from codegraph_explore's PascalCase type-disambiguation bias
(reporter's suggestions #1/#2) — unless it's the only query word, so a bare
project-name search still scores.

Narrow by construction: the down-weighting fires ONLY when a query word
matches the derived project name (≥5 chars), so every query that doesn't
name the project is byte-identical. On the reporter's repro the backend
controllers now top a backend question that includes the project name;
queries without it, bare project-name queries, and normal symbol queries
are unchanged. Query-time only (no re-index).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/index.ts

@@ -49,6 +49,7 @@ import { Mutex, FileLock } from './utils';
 import { FileWatcher, WatchOptions, PendingFile, LockUnavailableError } from './sync';
 import { EXTRACTION_VERSION } from './extraction/extraction-version';
 import { getCodeGraphDir } from './directory';
+import { deriveProjectNameTokens } from './search/query-utils';
 import { CodeGraphPackageVersion } from './mcp/version';
 
 // Re-export types for consumers
@@ -154,6 +155,13 @@ export class CodeGraph {
     this.db = db;
     this.queries = queries;
     this.projectRoot = projectRoot;
+    // Down-weight the project name as a query term in search ranking — it names
+    // the whole repo, not a symbol, so it has no discriminative value (#720).
+    try {
+      this.queries.setProjectNameTokens(deriveProjectNameTokens(projectRoot));
+    } catch {
+      // Best-effort: ranking still works without it.
+    }
     this.fileLock = new FileLock(
       path.join(getCodeGraphDir(projectRoot), 'codegraph.lock')
     );
@@ -747,6 +755,17 @@ export class CodeGraph {
     return this.queries.searchNodes(query, options);
   }
 
+  /**
+   * Normalized project-name tokens (go.mod / package.json / repo dir) used to
+   * down-weight the non-discriminative project name in search ranking (#720).
+   * Exposed so explore can exclude it from the PascalCase type-disambiguation
+   * bias, which would otherwise pull overloaded tokens toward whichever stack
+   * embeds the project name.
+   */
+  getProjectNameTokens(): Set<string> {
+    return this.queries.getProjectNameTokens();
+  }
+
   /**
    * Find the project's "primary route file" — the file with the densest
    * concentration of framework-emitted `route` nodes (≥3 routes, ≥30%