v0.51.0 — Settings shell, data-source grid and search payload

[0.51.0] - 2026-10-21

Search settings edits reach the retrieval request

• Discovered and fixed a real payload bug: the settings drawer marked the
  similarity-threshold and vector-weight sliders with their element ids
  (thresh/vWeight) while the retrieval builder checked threshold/weight,
  so edited slider values never reached the request. ssTouch now records the
  canonical keys too; the probe confirms an untouched request relies on the
  saved search app config and an edited request carries the new threshold.
• The user-setting shell now uses the upstream geometry exactly: a 303 px
  sidebar from the md breakpoint and 64 px below it, with the active item
  derived from the route and kept in sync across back/forward navigation.
• The data-source grid uses the upstream breakpoint set (1 column, 2 columns
  from 1024 px, 4 columns from 1536 px) instead of container queries that never
  reached the 4-column layout; the upstream page has no per-source search box,
  so the old residual is withdrawn.
• Re-audited the UI route table: all /chunk views, the chat widget embed and
  the agentbots log endpoint are registered and reachable, so the routes row is
  aligned.