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/term_msg.rs

@@ -101,14 +101,13 @@ impl TermMsg {
 /// Per-connection/per-request classification state. A live SSE stream keeps
 /// one of these alive for the connection's lifetime — `tool_use` id → name
 /// correlation, so a `tool_result` can tell it's answering a `recv` call and
-/// render as a default-open markdown message body. The history endpoint
+/// render its body as markdown instead of plain text. The history endpoint
 /// uses a fresh one per page: correlation only works within the page
 /// actually returned, not across the live/history boundary. Accepted
-/// degradation (same shape as the turn-timestamp fallback documented in
-/// `docs/terminal-rendering.md`) — the only user-visible effect is a `recv`
-/// result whose `tool_use` fell on the other side of a page/reconnect
-/// boundary rendering as a plain block instead of default-open markdown,
-/// not a functional loss.
+/// degradation — the only user-visible effect is a `recv` result whose
+/// `tool_use` fell on the other side of a page/reconnect boundary rendering
+/// its body as plain text instead of markdown (open/collapsed state is a
+/// uniform client-side preference either way, not affected by this).
 #[derive(Default)]
 pub struct ClassifyCtx {
     tool_name_by_id: HashMap<String, String>,