v0.34.0 — self_test probes the read path

Added

• self_test now reads the index and reports degraded when a search could
  not (#6). It returned a static snapshot of the contract and never opened
  the index, so a table that semantic_search could not read (#5) still
  reported ok. It now runs up to 10 rows of each source kind, per scope,
  through the code a search runs on a row (scoring, the result card and its
  payload) and returns read_probe with a state of ok or failed for
  project and global. A failed scope names the first row that broke
  (item_id) and the error, and sets status to degraded. The probe is
  read-only and needs no embedder: it never syncs, backfills or builds an
  index. Rows are sampled by kind because a sync writes every markdown block
  before the notes, so a plain head sample would never reach a damaged note.
  A note whose JSON is gone is counted in rows_skipped, as a search skips
  it. If the probe itself crashes, read_probe is {"state": "unavailable"}
  with the error and status stays ok. health is unchanged on purpose: it
  is a liveness check with no access to the store.