v0.1.0a2

Changed

• Completion is computed by key from the store, not from an index. A
  simulation is complete iff every output it is configured to produce exists
  (stilt.completion.is_complete). When wind-error params are set, that set
  includes the error trajectory.
• The registry is now .stilt/manifest.parquet (stilt.manifest) — a small
  parquet of registration metadata (sim_id / met / receptor / scene /
  footprints), read and written through the Store so it works on local
  filesystems and cloud object stores alike. Registration metadata only;
  completion is never stored.
• model.index → model.queue. The Postgres backend is now a lean,
  status-only work queue (stilt.service.PostgresQueue: enqueue → claim
  [FOR UPDATE SKIP LOCKED] → done/failed), present only when PYSTILT_DB_URL
  is set. Local projects have no database — registry is the manifest, completion
  is by key.
• Error-trajectory backfill runs only the error pass. Enabling error params
  on a project that already has trajectories now runs the error trajectory
  alone — reusing the existing main when the config (ignoring error params)
  matches — instead of recomputing every main trajectory.

Removed

• The stilt.index subpackage, SimulationIndex / IndexCounts /
  OutputSummary, the SQLite index backend, and the SQL
  completion-predicate / dialect machinery. The on-disk index database is gone.

Fixed

• A simulation with a main trajectory and footprints but no error trajectory
  (when wind-error params are configured) was incorrectly treated as complete and
  skipped under skip_existing. It is now re-dispatched so the error trajectory
  is backfilled.