The intent prompt override logic in query_understand applied
strings.TrimSpace to the value before assigning it as the system prompt
override, which silently stripped trailing newlines and intentional
formatting from agent-supplied prompts. Use TrimSpace only to detect
emptiness (so whitespace-only strings still fall back to the global
default) while passing the raw string through verbatim.
Extract the resolution into applyIntentPromptOverride and add unit tests
covering agent-wins, whitespace preservation, blank fallback, no-config,
and global-only paths.