title detection improvements

* special rule for first line
* detect preamble when no first line, drop down to "first sentence" rules (e.g. if first sentence only contains a single phrase emphasized via bold or wiki-links, use that as title)
* fall back to prompt (if prompt not long)
* quote/elaborate prompt classification

also:

```

/*
looks like we've got a bunch of records here where section
headers were tagged as title proposals.

"Definition","73"
"Overview","60"
"Key Concepts","47"
"Formal Definition","9"
"Core Concepts","8"
"Background","8"
"Mathematical Formulation","8"
"Fundamental Concepts","7"
Historical Context
Mathemtical Definition
Mathematical Framework
Formal Statement
Basic Concepts
Roadmap
Core Mechanisms & Doctrines
Mathematical Formalism
Key Components
Mathematical Formalization
General Setup
Key Characteristics

1. ...
Chapter 1. ...
*/
```

No files, tests, or entry points are named. Start by locating the title-detection and title-proposal classification logic, then turn the listed first-line, preamble, first-sentence, prompt, and section-header examples into regression cases. Done means the proposed rules select useful titles and stop treating headings such as “Definition” or “Overview” as titles.

Written by the indexing model from the issue text.