docs: fix write-good.So/ThereIs/Weasel lint findings

Fixes the "obvious ones first" slice of #4042 (mara: do the obvious
ones first) -- 81 hits across write-good.So, write-good.ThereIs, and
write-good.Weasel, all in docs/. Each is a genuine sentence rewrite
(lead with the real subject instead of "There is/are", drop a
sentence-initial "So ", replace a vague intensifier), not a blind
regex substitution -- read every hit in its real file context before
touching it.

3 of the 81 hits were in CI-generated CLI docs (docs/tools/{hivectl,
swarmctl,forge}-cli.md) -- fixed at the clap #[arg(...)]/doc-comment
source in hivectl/src/cli.rs, swarmctl/src/main.rs, and
hive-forge/src/verbs/repo_add_collaborator.rs, then regenerated via
each crate's `markdown-docs` subcommand so CI's freshness check stays
green.

Verified: fresh vale re-run shows 0 remaining So/ThereIs/Weasel hits
and no new hits introduced (983->982, exactly the one incidental fix
this pass also picked up at docs/scheduler/observability.md:48).
cargo fmt --check and clippy clean on the three touched crates.

Remaining write-good backlog (Passive: 726, TooWordy: 207) is
judgment-heavy and left for a follow-up slice of #4042, not bulk-
rewritten here.

docs/web-ui/agent.md

@@ -46,7 +46,7 @@ structurally rather than for one specific trigger. Two columns:
 - **Pills cluster** (`.agent-header-pills`, right-aligned): status
   badges (`StatusChips.tsx`) and flyout triggers together in one row —
   a deliberate choice (not the historical default) so the header reads
-  as one identity zone + one status/actions zone rather than several
+  as one identity zone + one status/actions zone rather than multiple
   separate clusters:
   - **Alive badge**: `● alive` (green) / `⊘ rate limited` (red) /
     `◌ needs login` / `◌ logging in` / `○ offline` / `… connecting`.
@@ -83,7 +83,7 @@ structurally rather than for one specific trigger. Two columns:
     (`GET /api/state`'s `links` field) also feeds
     `DashboardState.links` for the dashboard card's icon strip —
     `agent_links()` in hive-agent is the single source of truth for
-    both. There is no separate overflow (`⋯`) menu any more — it used
+    both. No separate overflow (`⋯`) menu exists any more — it used
     to hold exactly this dashboard link plus a rebuild-container action
     (mara, hyperhive#3704: "remove rebuild button, move link to
     dashboards into links menu") — rebuild had no real discoverability