chore(providers): reconcile the xKiro counts with the chipotle removal

The branch merged the release tip twice: the first pass carried a stale
origin/release/v3.8.51 that predated #13913, so every derived count was
computed against a provider that had already been retired.

Reconciled against the current tip:

- Provider count is 359 (tip 358 after the chipotle/pepper removal, plus
  xKiro). README, AGENTS.md, llm.txt and its 65 locale mirrors, package.json
  and the six count-bearing SVGs now carry that number; check:docs-counts
  passes with no strict drift.
- docs/reference/PROVIDER_REFERENCE.md regenerated from the live modules.
- RESERVED_PREFIX_COUNT 412 -> 413: xKiro registers id "xkiro" with no
  separate alias, so it adds exactly one REGISTRY member.

package.json

@@ -1,7 +1,7 @@
 {
   "name": "omniroute",
   "version": "3.8.51",
-  "description": "Unified AI router with 360 providers, RTK+Caveman compression, auto fallback, MCP/A2A, desktop, PWA, and OpenAI-compatible APIs.",
+  "description": "Unified AI router with 359 providers, RTK+Caveman compression, auto fallback, MCP/A2A, desktop, PWA, and OpenAI-compatible APIs.",
   "type": "module",
   "bin": {
     "omniroute": "bin/omniroute.mjs",