Source-group edit form gains pre/post hook textareas with a service-
user warning banner; bodies AEAD-encrypted on save (per-group AD).
Repo page adds a 'Host-default hooks' panel above the danger zone
with the same shape; saved via POST /hosts/{id}/repo/hooks.
Sources tab now lists every source group on the host with per-row
counts (used-by-N-schedules, snapshot count by tag), the v4
conflict tag (keep-* dimension that has no compatible cadence),
and Run-now / Edit / Delete actions. Run-now reuses the existing
HTMX-aware /hosts/{id}/source-groups/{gid}/run handler.
New /hosts/{id}/sources/new and /sources/{gid}/edit form: name +
includes/excludes textareas + the 3×2 keep-* retention grid +
retry-on-offline knobs. Server-side validation re-renders with the
operator's input intact; the inline conflict banner shows above the
retention grid when ConflictDimension is set.
Delete blocks (UI + server) when the group is referenced by any
schedule. Every successful mutation calls pushScheduleSetAsync so
an online agent re-arms within seconds.
Adds .src-row and .keep-cell to input.css for the row + retention
grid layout.
steve