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>

TELEMETRY.md

@@ -39,7 +39,7 @@ Every payload carries this envelope:
 | `os` / `arch` | `darwin` / `arm64` | platform identifiers only |
 | `node_major` | `22` | major version only |
 | `ci` | `false` | whether the `CI` env var was set |
-| `schema_version` | `1` | bumped when this page changes |
+| `schema_version` | `2` | bumped when this page changes (v2 dropped the `index` event's `sqlite_backend` field) |
 
 And one of four events:
 
@@ -48,8 +48,7 @@ And one of four events:
   an upgrade, or a re-run.
 - **`index`** — when a full index completes: the **language names** present (e.g.
   `["typescript","go"]`), the file count as a **coarse bucket** (`<100`, `100-1k`,
-  `1k-10k`, `10k+`), the duration as a bucket (`<10s`, `10-60s`, `1-5m`, `5m+`), and the
-  SQLite backend (`native`/`wasm`).
+  `1k-10k`, `10k+`), and the duration as a bucket (`<10s`, `10-60s`, `1-5m`, `5m+`).
 - **`usage_rollup`** — one line per day per tool: the tool or CLI command **name** (e.g.
   `codegraph_explore`, `init`), how many times it ran, how many errored, and — for MCP
   tools — the connecting agent's name and version from the MCP handshake (e.g.