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.

__tests__/identifier-segments.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 import {
   splitIdentifierSegments,
   extractProseCandidates,
+  extractSegmentSearchWords,
   normalizeProseWord,
   segmentLookupVariants,
 } from '../src/search/identifier-segments';
@@ -101,3 +102,32 @@ describe('segmentLookupVariants — light plural folding', () => {
     expect(segmentLookupVariants('boxes')).toEqual(['boxes']); // -es strip would go sub-minimum
   });
 });
+
+describe('extractSegmentSearchWords — query words for the search-side vocab supplement', () => {
+  it('keeps prose words and adds camel-token segments', () => {
+    const words = extractSegmentSearchWords('auto-scroll to bottom — atBottom tracking');
+    // Prose candidates survive as before…
+    expect(words).toContain('scroll');
+    expect(words).toContain('bottom');
+    expect(words).toContain('tracking');
+    // …and the camel token contributed its ≥4-char segments ("at" is under
+    // the prose minimum; "bottom" arrives from the split even when the prose
+    // pass missed it).
+    expect(extractSegmentSearchWords('where is atBottom set')).toContain('bottom');
+  });
+
+  it('splits multi-hump tokens into every usable segment', () => {
+    const words = extractSegmentSearchWords('trace pinFeedIfNearBottom please');
+    expect(words).toEqual(expect.arrayContaining(['feed', 'near', 'bottom']));
+  });
+
+  it('does not invent segments for plain prose', () => {
+    const words = extractSegmentSearchWords('how does checkout work');
+    expect(words).toContain('checkout');
+    expect(words).not.toContain('check');
+  });
+
+  it('returns nothing for an empty query', () => {
+    expect(extractSegmentSearchWords('')).toEqual([]);
+  });
+});