Fix stale default-open doc comments per argus's review

ClassifyCtx's tool_use-id correlation gates markdown-vs-plain body
format for a recv result, not open/collapsed state — that's always
the operator's uniform preference now. 5 backend comments still
described it as controlling "default-open" rendering, contradicting
the actual render path and this PR's own rewritten docs.

Also fixed useAgentState.ts's stale comment promising an
SSE-triggered refresh model "in a later commit" — that's permanently
off the table now that the terminal stream's kind tag is gone by
design (argus flagged this as a drive-by, not blocking, but it's a
one-line cause-and-effect of this same PR so fixing it here).

hive-agent/src/web_ui/stream.rs

@@ -79,9 +79,10 @@ pub(super) async fn events_history(
     // replay and live tail deliver identical shapes. The DB stores raw
     // events; classification is applied at read time here (see
     // `crate::term_msg`). One `ClassifyCtx` for the whole page — tool_use→
-    // name correlation (for default-open `recv` results) only works within
-    // a single page/connection, not across the live/history boundary; see
-    // that module's doc for why that's an accepted degradation.
+    // name correlation (for markdown-vs-plain `recv` result bodies) only
+    // works within a single page/connection, not across the live/history
+    // boundary; see that module's doc for why that's an accepted
+    // degradation.
     let mut ctx = ClassifyCtx::default();
     let events: Vec<TermEnvelope> = events
         .into_iter()