llm: restore request logging lost in the agent-loop migration

The LLM-requests page has been empty since 24ee5b8: deleting
`session/handler/llm_call.rs` dropped both halves of the request log.

The kernel builds the `ModelRequest` itself and sets `log: None`, so the
`LoggingModel` decorator — wrapped once per model by `LlmManager` — wrote
every metadata row with a NULL `user_id`, while the page (and the detail
endpoint) filter on it. Nothing wrote `llm_request_payloads` at all any
more, so the payload viewer had nothing to show either.

Correlation cannot come from `LlmManager`: it builds one shared client
per model and does not know whose traffic it serves. It now comes from
the `ModelSelector`, the one component that knows both the model and the
owner: `SkaldSelector::with_log(RequestLogTarget)` wraps the model it
hands out, so metadata lands in `llm_requests` attributed to the user and
the payload lands in that user's own encrypted DB, keyed by `request_id`.
Session and frame are read off the request's `conversation`/`frame`,
which makes kernel rounds, sub-agent frames and compaction summaries all
attributed with no extra plumbing (`ModelRequest::log` stays unused).

The compactor's summariser call is attributed too, which it never was:
`try_compact`/`force_compact` now take the owner (its selector is built
per compaction, so it can carry the target).

Three tests in `llm::logging` lock this down — the owner/session/frame
columns, the error row with the provider's rejected body, and the
metadata-only path when no owner pool is available.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/skald-core/src/session/handler/mod.rs

@@ -452,7 +452,8 @@ impl ChatSessionHandler {
         match self.compactor {
             Some(ref compactor) => {
                 compactor.force_compact(
-                    self.loop_runtime.manager(), pool, self.session_id, stack.id, self.is_ephemeral,
+                    self.loop_runtime.manager(), pool, &self.user_id,
+                    self.session_id, stack.id, self.is_ephemeral,
                 ).await
             }
             None => Ok(false),
@@ -555,7 +556,8 @@ impl ChatSessionHandler {
         if let Some(ref compactor) = self.compactor {
             let last_tokens = self.last_input_tokens.load(Ordering::Relaxed);
             match compactor.try_compact(
-                self.loop_runtime.manager(), pool, self.session_id, stack.id, last_tokens, self.is_ephemeral,
+                self.loop_runtime.manager(), pool, &self.user_id,
+                self.session_id, stack.id, last_tokens, self.is_ephemeral,
             ).await {
                 Ok(true)  => info!(session_id = self.session_id, stack_id = stack.id, "handle_message: context compacted"),
                 Ok(false) => {}