Surface LLM correlation fields in debug view; fix unit-continuity path

/admin/debug/correlation stripped corr_consensus and the corr_llm_* fields
that upload.py's consensus correlator writes onto the call doc, making it
the one tool built to answer "is the LLM correlation tier alive" unable to
answer it (2026-08-19 dump had to infer LLM state from commit dates instead
of reading it off the data). admin.py's _call_summary() now includes
corr_consensus, corr_llm_reasoning, corr_llm_action, corr_rules_action.

The unit-continuity correlation path never wrote corr_matched_units, unlike
fast/single and fast/disambig, so the debug view showed null for a match
that was in fact unit-driven by construction. Now populated unconditionally
on that path (server-26#16).

Also traced the negative corr_incident_idle_min (-4.1 observed) to its root
cause: the re-correlation sweep anchors `now` to the linking call's own
started_at, and that back-dated value was being written straight into the
incident's updated_at, letting it land before the incident's own
started_at. Added _floor_at_started_at() so updated_at can never precede
started_at. (commit 33a247d already fixed the recency *gates* misreading
that negative value; this fixes the write that produced it.) Verified the
skip_reason filter in recorrelation_sweep.py:63 is already correct, no
change needed there.

Added tests for the debug endpoint's LLM field passthrough, the
unit-continuity corr_matched_units fix, and the updated_at floor — each
confirmed to fail when its fix is reverted. 148 passed, 0 failed.

Closes logan/server-26#24
Closes logan/server-26#16

drb-c2-core/app/routers/admin.py

@@ -91,6 +91,14 @@ async def debug_correlation(
             "corr_matched_units":    call.get("corr_matched_units"),
             "corr_sweep_count":      call.get("corr_sweep_count"),
             "skip_reason":           call.get("skip_reason"),
+            # LLM consensus tier fields — written by upload.py's
+            # _correlate_with_consensus / llm_correlator.py, but previously
+            # dropped here, making it impossible to tell from this endpoint
+            # whether the LLM correlation tier is actually running (server-26#24).
+            "corr_consensus":        call.get("corr_consensus"),
+            "corr_llm_reasoning":    call.get("corr_llm_reasoning"),
+            "corr_llm_action":       call.get("corr_llm_action"),
+            "corr_rules_action":     call.get("corr_rules_action"),
         }
 
     # ── Determine which systems have AI active ────────────────────────────────