v0.8.1

diting v0.8.1

Search-stack batch, seven fixes in one release:

- merge quality: per-engine score rescale (verbosity no longer decides
  consensus), CN/social tracking-param dedup (18 params), highest-score
  title pick
- time_range end-to-end: native SERP filters for Baidu/Bing/Sogou/DDG
  plus merge-time demotion for engines without date filtering
- overall search deadline: DITING_SEARCH_DEADLINE_SECS (default 9s);
  late engines surface as slow in engine_errors
- persistent search cache: the SQLite searches table finally gets a
  reader — restarts stop re-paying the network
- engine health: 3 consecutive transients cool an engine 90s; post-
  cooldown probation merges its hits at half weight until one clean
  success; /engines exposes streak and probation
- section-located snippets: hits against cached pages prefix their
  snippet with [§ heading] — the agent sees where on the page the
  match landed

Engine batch: UA default link color, upload MIME inference from
extension, XHR abort/reentrancy contract tests. Memory figures
re-measured: ~25 MB cold start, <40 MB steady static use.