feat(render): compact search results and bounded page contents - #49

The description matches the diff: the new `RenderOptions`/`render_*_with` surface, the `compact()` preset, and `ProviderConfig.contents_max_chars` (including the 1,500-character clamp and the default preserving today's 500-char output) are all described, and the README documents both. The change looks sound to merge; the only nit is that the body's gate list doesn't mention the repository's `cargo fmt`/`--all-features` commands, which is not a defect in behaviour.

No findings.