fix(client): value-based dirty tracking and guarded section saves

Make useSectionForm derive isDirty by comparing current values with a
saved-values snapshot instead of TanStack's meta-based flag: programmatic
auto-select writes ({dontUpdateMeta:true}) are real unsaved changes the
meta flag can never see, while async-default rebases left it stuck true
and triggered reload alerts on untouched forms. Guard persistSection so
an untouched section never reaches the network - repeater expand/collapse,
tab switches, and save buttons all funnel through it now. Drop the
form.reset from useSyncFormDefaults (it could revert same-frame keystrokes
and silently cleared touched state); it only rebases the snapshot.