docs: fix capitalization losses + one text corruption from the contractions pass

Review pass on top of the previous commit (85a94671) turned up three
real issues its own vale-only verification didn't catch:

- 'has not' -> 'hasn't' fired inside 'has nothing', corrupting
  docs/swarm/README.md into 'hasn'thing to say upward'. Restored
  'has nothing'.
- ~44 hits where the original text was genuinely sentence-initial
  ('It is', 'That is', 'They are', 'What is', 'Do not', ...) got
  contracted in lowercase, silently de-capitalizing the start of a
  sentence. Checked each one's real surrounding text and capitalized
  the ones that needed it.
- Confirmed (by reading the actual text, not just trusting vale) that
  the 3 remaining 'is not'/'has not'/'it is' hits after those fixes are
  vale's own false positives: it matches these as a bare substring with
  no trailing word boundary, so it also fires on 'is nothing', 'has
  nothing', and the already-correct 'it isn't'. Left those alone --
  there's no real issue in the text.

Re-verified with a fresh vale run: the remaining 17 hits are exactly
the union of the 14 legitimate ALL-CAPS/bold-emphasis skips from the
first commit and these 3 false positives. Full accounting in
/agents/iris/state/haiku-batches/contractions-report.md.

docs/web-ui/dashboard.md

@@ -852,7 +852,7 @@ life). Two consequences for anything rendering it:
   string; don't switch on specific values. `restarting` in
   particular no longer exists, because no node kind is unique to a
   restart.
-- it's **not** exclusively operator-initiated, and **not** limited
+- It's **not** exclusively operator-initiated, and **not** limited
   to rebuild-shaped work — `running_transients()` on the backend is
   a status-only test (any `Running` node whose payload names a
   non-empty agent lights a pill), so work the operator never