ci: run tests on Node 26, not 24 (node:sqlite teardown segfault)

The test job segfaulted on Node 24 (exit 139) during jest's --forceExit
teardown, after all tests passed — the crash is in node:sqlite's native
teardown, which the RAG/knowledge-base suites exercise via the real in-memory
DB harness.

Reproduced locally with a downloaded Node 24.18.0 vs system Node 26, running
the full suite (--coverage --forceExit --runInBand):
  - Node 24: exit 139 (segfault), with AND without an attempt to close every
    sqlite handle in teardown — so it is not our open handles, it is Node 24's
    node:sqlite teardown path.
  - Node 26: exit 0, 532 suites / 7817 tests pass, coverage gate green.

Node 26's node:sqlite fixes the teardown crash, so pin the test runtime to 26.

Author: alichherawalla

.github/workflows/ci.yml

@@ -136,11 +136,13 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          # Node 24: the RAG/knowledge-base suites run a REAL in-memory database via
-          # node's built-in `node:sqlite` (__tests__/harness/sqliteFake.ts). That module
-          # is unavailable on Node 20 and flag-gated on Node 22; it is available without a
-          # flag from Node 23.4+, so the test runtime is pinned to 24.
-          node-version: '24'
+          # Node 26. The RAG/knowledge-base suites run a REAL in-memory database via node's
+          # built-in `node:sqlite` (__tests__/harness/sqliteFake.ts). That module is absent on
+          # Node 20 and flag-gated on Node 22. On Node 24 it loads but its native teardown
+          # SEGFAULTs the process under jest's --forceExit (exit 139) — reproduced locally: the
+          # full suite exits 139 on Node 24 and exits 0 on Node 26. Node 26's node:sqlite fixes
+          # that teardown crash, so the test runtime is pinned to 26.
+          node-version: '26'
           cache: 'npm'
 
       - name: Setup Java