docs(vex): split vex into its own reference, refresh for v1.16.0

- Add vex.md: install (prebuilt binaries + self-update), GPU/CUDA setup,
  jina-code+CUDA recommendation (CUDA essential, too slow on CPU),
  vex mcp install, full command set (bundle/paths/reachable/diff/history,
  search scope+metadata filters), CLAUDE.md integration, caveats
- Shrink claude-code-tools.md section vex to a blurb + links
- Note v1.16.0 capabilities in the vex-vs-ast-index benchmark (not re-benchmarked)
- README: bump date, index vex.md, refresh vex descriptions

code-search-vex-vs-ast-index.md

@@ -11,6 +11,24 @@
 > this revision. See ["Changes since the 2026-05-18 snapshot"](#changes-since-the-2026-05-18-snapshot)
 > at the bottom for a summary.
 
+> **Capability update — vex 1.16.0 (capabilities only, NOT re-benchmarked):** the
+> latency and quality tables below remain pinned to **vex 1.9.1**, but vex's feature
+> surface has moved on. New since 1.9.1 (no fresh measurements taken here):
+>
+> - **`vex history <Symbol>`** (v1.16) — query-time git-log walker returning every
+>   historical version of a symbol (`--diff`, `--since`/`--until`, `--author`, `--kind`);
+>   opt-in indexed sidecar via `vex index --history`. No ast-index equivalent.
+> - **`vex mcp install` / `uninstall` / `list`** (v1.15.0) — idempotent MCP-server
+>   registration for Claude Code / Cursor (replaces hand-editing the agent config).
+> - **Scope & metadata search filters** on `vex search` / `vex usages` — `--kind`,
+>   `--include`/`--exclude`, `--since`/`--since-branched`/`--changed-only`, `--visibility`,
+>   `--async-only`, `--static-only`, `--sealed-only`, `--why`.
+> - **`vex gpu`** execution-provider probe; **`vex watch`** continuous reindex;
+>   **`vex init --agents-md`**; prebuilt Windows `vex` + `vex-mcp` binaries.
+>
+> See **[vex.md](vex.md)** for the full current reference (install, GPU/CUDA, config,
+> command set). Re-run the tables below on 1.16.0 before citing the numbers.
+
 ## Test environment
 
 | Aspect | Value |
@@ -94,6 +112,7 @@ Three real queries from the test repo (re-run on 2026-05-26):
    - `vex bundle --mode {symbol,pr-impact,project}` — one call replaces the `show → callers → callees → similar` round trip; pr-impact mode bundles changed symbols + transitive callers + reachable tests for code review.
    - `vex eval` — built-in ranking eval harness for CI regression.
    - `vex capabilities` — machine-readable feature matrix.
+   - **Since v1.10–v1.16 (see the capability-update note at the top + [vex.md](vex.md)):** `vex history` (symbol-level git archaeology), `vex mcp install`/`uninstall`/`list` (idempotent MCP registration), `vex gpu` (EP probe), `vex watch` (continuous reindex), and scope/metadata search filters (`--kind`, `--include`/`--exclude`, `--since`/`--changed-only`, `--visibility`, `--async-only`, `--why`).
 
 ## Practical recommendation