Prevent conversational titles for bare link tasks

Task 9264's body was just "Fix https://app.jaah.ai/tasks/9255?tab=activity". Its generated title came out as "I can see you've provided a link", which is an LLM chat reply, not a title. - When the body is only a link (or a link plus a verb), the generated title should name the link's target, e.g. "Fix task 9255 Activity". - When the title model answers conversationally ("I can see…", "Sure", "It looks like…"), discard that and fall back to a truncated first line of the body. Out of scope: the "Re-generate title" button itself, and title editing. Done means: a task created with the body "Fix https://app.jaah.ai/tasks/9255?tab=activity" gets a title that names task 9255, and a unit test covers the conversational-reply fallback.

Bare-link bodies are now titled from the link ("Fix task 9255 Activity"), and chat-style model replies fall back to the body's cut first line. Quick gate and 125 changed-area tests pass. PR #6723 is queued to the merge lane. Memory: used mem-15203; proposed none.