docs(code-search): refresh vex vs ast-index notes for vex 1.9.1 / ast-index 3.41.0

- Re-bench on 2026-05-26 against vex 1.9.1 and ast-index 3.41.0.
- Flag findings that flipped vs the 2026-05-18 snapshot:
  - ast-index Python call graph now populated (was empty in 3.27)
  - vex implementations now handles generic-parameterized subclasses (v1.7.0)
  - vex usages is now AST-precise on T1 languages; ast-index is now the
    textual-match tool, inverting the old precision finding
  - vex now has diff --base <rev>, making the "only ast-index has
    changed --base" finding obsolete
  - vex now ships prebuilt Windows binaries; vex self-update works
- Document new vex 1.5 -> 1.9 commands: diff, paths, reachable, check,
  bundle (symbol/pr-impact/project), eval, self-update, capabilities.
- Add README entry for the doc; it was previously missing from the index.
- Bump README "Last updated" to 2026-05-26.

README.md

@@ -1,6 +1,6 @@
 # Claude Code Facts
 
-> Last updated: 2026-05-18
+> Last updated: 2026-05-26
 
 A collection of interesting and useful facts, tips, tools, and guides for working with Claude and Claude Code.
 
@@ -25,3 +25,7 @@ Review of code signing options for Windows executables — Azure Trusted Signing
 ### [Gitea Act Runner — Worker Capacity (TrueNAS)](gitea-runner.md)
 
 How to configure parallel job capacity for Gitea Act Runner on TrueNAS. Covers the `CONFIG_FILE` env var requirement, custom `config.yaml` mount, and capacity tuning.
+
+### [Code Search: vex vs ast-index — Benchmark Notes](code-search-vex-vs-ast-index.md)
+
+Point-in-time benchmark of `vex` and `ast-index` on a real mixed-language repo — indexing footprint, query latency, precision findings, and when to fall back from one to the other. Refreshed for `vex 1.9.1` / `ast-index 3.41.0`, with a summary of what flipped since the previous snapshot.