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/trust-boundary/boundary.md

@@ -110,7 +110,7 @@ agent's container uid/gid** — `o=--x` is traverse without listing, and
 both sockets are `0666`, which is all a dialer needs.
 
 **Ownership is declared, not repaired.** The tmpfiles.d entry written by
-`SyncAgentTmpfiles` names the uid/gid directly. don't add a chown
+`SyncAgentTmpfiles` names the uid/gid directly. Don't add a chown
 alongside it: `d` re-applies on every boot _and_ every agent
 spawn/destroy, so ownership set afterwards is reverted the next time any
 agent changes — which is exactly how this dir spent a long time at

docs/trust-boundary/security.md

@@ -5,7 +5,7 @@
 The sections below document specific mechanisms (the state-file endpoint,
 nixbld isolation, privilege separation). This section frames the model they
 serve: **what hyperhive defends, what it deliberately doesn't, and where the
-operator is accepting risk.** it's the reference for "is it safe to give an
+operator is accepting risk.** It's the reference for "is it safe to give an
 agent capability X?".
 
 ### The trust boundary is the container, not credential storage
@@ -66,7 +66,7 @@ checkpoints**, not about sandboxing the agent from its own tools:
   merges restricted to the operators team + a required operators-team approval
   (`apply_operator_branch_protection` / the config-repo equivalent) — and an
   agent (a write collaborator, not a repo admin) can neither change those
-  settings nor merge its own PR. it's **not** set up for external VCS (GitHub
+  settings nor merge its own PR. It's **not** set up for external VCS (GitHub
   etc.), though — there, operator-merge is process + accepted risk, not a
   technical control.
 - **Approvals** — config changes, schedule additions, and other
@@ -161,7 +161,7 @@ services — including the core dashboard at `127.0.0.1:<dashboard_port>`, which
 has no application-layer auth of its own (see [`docs/scheduler/ci.md`](../scheduler/ci.md)). The `0600`
 token policy bounds file reads; network isolation bounds network reach.
 
-**what's NOT exposed**:
+**What's NOT exposed**:
 
 - `/home/<name>/.claude/` — mode `0700`, owned by the per-agent
   user `<name>`. nixbld users can't read it.
@@ -171,7 +171,7 @@ token policy bounds file reads; network isolation bounds network reach.
   can't read it.
 
 **Policy**: all credential files written to agent state directories MUST be mode
-`0600` or stricter. don't create world-readable secret files in agent state dirs.
+`0600` or stricter. Don't create world-readable secret files in agent state dirs.
 
 ### Long-term fix