fix(explore): accurately resolve query file paths and find camelCase symbols

Previously, `codegraph_explore` queries explicitly naming files by path (e.g., `src/routes/m/projects/[id]/runs/[runId]/+page.svelte`) were shredded. Bracketed path segments exploded into "named symbol" seeds, and FTS on fragments like `page` or `runs` admitted every sibling file, starving the user's intended target.

This change introduces:
- **Query path pinning:** File paths named in a query are now resolved against the index, "pinned," and stripped from the query. Pinned files are guaranteed inclusion, top ranking, and fair allocation. Unresolvable path-like spans are reported.
- **Segment vocabulary supplement:** Natural language query terms (e.g., "auto-scroll to bottom") can now reach camelCase identifiers (e.g., `pinFeedIfNearBottom`, `feedAtBottom`) by matching against their constituent segments.
- **Variable seeding:** `variable` and `constant` node kinds are now included in identifier seeding, improving recall for `$state`-style variables common in frameworks like Svelte.

src/mcp/explore-diagnostics.ts

@@ -60,6 +60,8 @@ export interface ExploreCandidateMeta {
   graphScore: number;
   termHits: number;
   nodes: number;
+  /** The query named this file by PATH — pinned rank/allocation treatment. */
+  pinned?: boolean;
   named: boolean;
   central: boolean;
   entry: boolean;
@@ -579,6 +581,7 @@ export class ExploreDiagnostics {
           graphScore: round6(r.graphScore),
           termHits: r.termHits,
           nodes: r.nodes,
+          pinned: r.pinned ?? false,
           named: r.named,
           central: r.central,
           entry: r.entry,
@@ -797,6 +800,7 @@ export function renderTable(report: ExploreDiagnosticReport): string {
 
 function flagString(f: ExploreDiagnosticFile): string {
   const flags: string[] = [];
+  if (f.pinned) flags.push('pinned');
   if (f.named) flags.push('named');
   if (f.entry) flags.push('entry');
   if (f.central) flags.push('central');