fix(inplace,embed): input set back mid-flight, report inputs, ambiguous anchors

Four items owed after S5b, reported by design-dev during the anti-slop run:

- carry() measured a sent-then-changed form against its OLD DEFAULTS. An
  answer set back mid-flight to the value the page first showed read as
  untouched, and the swap put the just-saved value over it. A form sent and
  then changed is now measured against its sent snapshot (sentSet.snapOf).
- The embed's clean-batch reload saw only our own forms. A report's own
  inputs lost whatever the operator had typed into them. Unsaved text in
  any control we don't own now holds the reload, and the page says so.
- Two r2b.toml rows ("D3 a stored theme...", "D3 forced light...") matched
  twice, so they proved only by where the first match fell. Both are
  re-anchored, and scripts/mutation_check.py now refuses any anchor that
  matches more than once. A new tool control covers that.
- The r2_flow contract's C3 steps 2 and 4 now say what S5b superseded. U3
  gains the report-input rule.

Mutation rows: u3_submit_all +1, r2_submit_all +1. Four rows were
re-anchored onto the moved lines.

tests/mutations/r2_flow.toml

@@ -126,7 +126,7 @@ new = ''''''
 label = 'C3 client: an unsent radio is not carried across a swap'
 file = "booth/templates/base.html"
 test = "tests/test_flow_browser.py::test_an_unsaved_choice_survives_a_save_elsewhere_and_a_double_click_writes_once"
-old = '''          if (el.checked !== el.defaultChecked) t.checked = el.checked;'''
+old = '''          if (el.checked !== on) t.checked = el.checked;'''
 new = ''''''
 
 [[mutation]]