fix: installSpawnCli fails on Sprite — bun shim doesn't work (#2993)

Sprite has a bun shim at /.sprite/bin/bun that delegates to
$HOME/.bun/bin/bun, but that binary doesn't exist on fresh VMs.
`command -v bun` returns true (finds the shim) so the install script
skips bun installation, then bun fails when actually invoked.

Fixed in two places:
- installSpawnCli: source shell profiles, test `bun --version` (not
  just existence), and install bun fresh if it doesn't work
- install.sh: replace `command -v bun` with `bun --version` to detect
  broken shims

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@openrouter/spawn",
-  "version": "0.26.4",
+  "version": "0.26.5",
   "type": "module",
   "bin": {
     "spawn": "cli.js"