v0.4.0 — recall returns memories

• Recall returns memories. RecallResult.Hits becomes Memories, and
  each entry is one whole memory with its Content rather than a scattering
  of its sections. Matched names the arms that found it, Sections the
  headings that matched, Via what pulled in a neighbour.
• Scores mean something. Score is calibrated in [0, 1] and comparable
  across queries, replacing a fused rank that only ordered one response.
  Scores.Coverage says how much of the query a memory accounted for.
• RecallOptions carries filters — Tiers, Paths, Tags, TagsAll,
  Since, Until, MinScore, NoContext, Detail, IncludeExpired —
  applied inside every retrieval arm server-side rather than after the fact.
• Answer returns one text answer: a fast model over a retrieval, or with
  ModeAgentic a stronger model that searches the memory itself with tools
  and returns its Trace. Returns ErrNoAnswer rather than an empty string.
  Both meter as chats.
• Vocabulary — LearnTerms, Vocabulary, LookupTerm, ForgetTerms. A
  learned alias makes a query for any surface form find memories written with
  another; matched definitions come back as Defined.
• Skills — StoreSkills and FindSkills, stored as memories under the
  skills/ tier.
• Candidates, FilteredOut and Timings report what retrieval did.