fix: import getMaxToolUseConcurrency into local scope and add ripgrep fallback (#8)

toolOrchestration.ts used `export { getMaxToolUseConcurrency } from
'./toolConcurrency.js'` (a re-export) but then called the function
directly in runToolsConcurrently(). A re-export does not bring the name
into the module's own scope, causing a ReferenceError at runtime —
visible as "getMaxToolUseConcurrency is not defined" in --print mode.
TypeScript also flagged this as TS2304 on main.

Fix: replace the re-export with an explicit import + a separate export
statement so the name is both locally callable and publicly exported.

ripgrep.ts fell through to the vendor binary path on non-bundled (npm)
installs where the vendor/ directory is not shipped alongside dist/cli.mjs,
producing "spawn .../vendor/ripgrep/x64-linux/rg ENOENT". Fix: check
whether the vendor binary exists before returning the builtin config;
fall back to system rg if it is absent.

src/services/tools/toolOrchestration.ts

@@ -4,10 +4,11 @@ import { findToolByName, type ToolUseContext } from '../../Tool.js'
 import type { AssistantMessage, Message } from '../../types/message.js'
 import { all } from '../../utils/generators.js'
 import { type MessageUpdateLazy, runToolUse } from './toolExecution.js'
-export {
+import {
   DEFAULT_MAX_TOOL_USE_CONCURRENCY,
   getMaxToolUseConcurrency,
 } from './toolConcurrency.js'
+export { DEFAULT_MAX_TOOL_USE_CONCURRENCY, getMaxToolUseConcurrency }
 
 export type MessageUpdate = {
   message?: Message