perf(resolution): fix O(K²) import-node blowup in "Resolving refs" (#915) (#965)

* perf(resolution): resolve imports to definitions, not sibling import nodes (#915)

"Resolving refs" crawled (tens of minutes) on large projects — most painfully
ones mixing a big front-end and back-end. An external package or module imported
across hundreds/thousands of files (react, a shared UI package, Python
logging/typing) is re-declared as an `import` node in every importing file, so
its unresolved import ref fell through to the exact-name matcher, which scored
all K same-named import nodes via findBestMatch — K refs x K candidates = O(K^2)
per package, producing only meaningless import->import edges.

Fix: exclude `import`-kind nodes as name-match targets (they're statements, not
definitions; real import->definition resolution is the import resolver's job).
Plus two safe constant-factor wins in findBestMatch: hoist the per-candidate
ref.filePath split, and skip cross-language candidates when a same-language one
exists (provably the same winner — same-language scores >=50, cross-language
maxes at 35).

Measured: superset (Py+TS) candidates scored 7.5M -> 833K (9x), non-import edges
preserved (+1618 now resolve to real defs), ~22K useless import->import edges
removed; kubernetes (Go) computePathProximity 37.2s -> 5.0s; synthetic 8k-file
mixed repo (K=4000) resolution 16.0s -> 1.7s. Full suite green.

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

* docs: correct stale better-sqlite3/wasm references to node:sqlite

The SQLite backend has been Node's built-in node:sqlite (real SQLite, WAL + FTS5,
from the bundled runtime) for a while — there is no native build step and no
node-sqlite3-wasm fallback. README and the docs site were already updated; this
catches the stragglers:

- CLAUDE.md: the src/db/ backend description and the sqlite-backend test note.
- src/db/index.ts, src/mcp/tools.ts: two code comments that still blamed "the
  wasm backend" for non-WAL behavior (reworded to "when WAL isn't in effect").

Leaves tree-sitter grammar wasm (web-tree-sitter / --liftoff-only) untouched —
that's a different, still-current use of wasm.

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

* chore(telemetry): drop the dead sqlite_backend field (schema v2)

node:sqlite is now the only backend, so the `index` event's `sqlite_backend`
field was a constant ("native") carrying no signal — and the `install` event
never actually sent it. Remove the field and the backendKind() helper, bump the
telemetry SCHEMA_VERSION 1 -> 2, and update TELEMETRY.md + docs/design/telemetry.md.

The ingest worker is deliberately left tolerant: `index` doesn't require the
field and schema_version validates as nonNegInt(99), so v2 events ingest fine and
old clients still sending v1 + sqlite_backend keep validating too. Added a legacy
comment there explaining it's safe to drop once old-client share is negligible.

telemetry.test.ts: the assertion pinning schema_version and a stale-claim fixture
line updated 1 -> 2. All telemetry tests pass.

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

---------

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

__tests__/telemetry.test.ts

@@ -173,7 +173,7 @@ describe('Telemetry', () => {
       expect(calls).toHaveLength(1);
       const body = calls[0]!.body;
       expect(body.machine_id).toBe(t.getStatus().machineId);
-      expect(body.schema_version).toBe(1);
+      expect(body.schema_version).toBe(2);
       const events = body.events as Array<{ event: string; ts: string; props: Record<string, unknown> }>;
       expect(events).toHaveLength(2);
       const explore = events.find((e) => e.props.name === 'codegraph_explore')!;
@@ -265,7 +265,7 @@ describe('Telemetry', () => {
       const t = make();
       const stale = path.join(dir, 'telemetry-queue.sending.99999.jsonl');
       fs.mkdirSync(dir, { recursive: true });
-      fs.writeFileSync(stale, JSON.stringify({ v: 1, ev: 'uninstall', ts: '2026-06-11T00:00:00.000Z', props: {} }) + '\n');
+      fs.writeFileSync(stale, JSON.stringify({ v: 2, ev: 'uninstall', ts: '2026-06-11T00:00:00.000Z', props: {} }) + '\n');
       const old = new Date(nowValue.getTime() - 2 * 60 * 60_000);
       fs.utimesSync(stale, old, old);
       t.setEnabled(true, 'cli'); // config so send() has a machine id