fix(cookbook): stop Ollama runner from executing the install one-liner (#3926)

The generated bash runner printed the missing-ollama hint with the install
one-liner wrapped in backticks inside a double-quoted echo. Backticks in
double quotes are command substitution, so on any serve target without
ollama the script downloaded and ran the system-wide installer (including
remote SSH hosts) instead of printing the hint. _validate_serve_cmd rejects
backticks in user-supplied commands for exactly this reason; the app's own
generated script never goes through that validator.

Move the hint into OLLAMA_MISSING_HINT in cookbook_helpers (no substitution
tokens) and emit it single-quoted via _bash_squote. Tests assert the hint
has no expansion tokens, that no generated echo line carries backticks
inside double quotes, and that bash prints the line literally.

Fixes #3816

routes/cookbook_helpers.py

@@ -558,6 +558,18 @@ def _bash_squote(v: str) -> str:
     return v.replace("'", "'\\''")
 
 
+# Shown by generated runner scripts when the ollama binary is missing on the
+# target host. Must stay free of backticks/$( ) and be emitted single-quoted:
+# an earlier version wrapped the install one-liner in backticks inside a
+# double-quoted echo, which bash executed as command substitution and ran the
+# system-wide installer (including on remote SSH hosts) instead of printing
+# the hint.
+OLLAMA_MISSING_HINT = (
+    "ERROR: Ollama not found on this server. Install it from "
+    "https://ollama.com/download or run: curl -fsSL https://ollama.com/install.sh | sh"
+)
+
+
 # Allow-list of binaries permitted as the leading token of `req.cmd` for /api/model/serve.
 # Anything else is rejected before the cmd is interpolated into a tmux/PowerShell wrapper.
 _SERVE_CMD_ALLOWLIST = {