feat(brain): surface an aging review queue in brain_context (#82)

brain_pending existed the whole time four real items sat unreviewed from
2026-04-23 to 2026-07-15. The tool was never the gap — nothing ever
prompted anyone to call it. The system should be what remembers the queue
exists.

Option 2 from the issue: ride along with brain_context, which sessions
already call, so noticing an aging note costs nobody a decision to go
looking. No scheduled job, no ntfy wiring, nothing new to keep running.

Threshold-gated at 14 days, and silent below it — a notice on every
context call is one people learn to skip, which reproduces the original
failure with extra steps. It reports the whole queue once it speaks: the
threshold decides whether to talk, not what to count.

It never promotes, rejects or reorders. Age is a reason to ask a human,
not a verdict; an old note may be exactly right to promote once someone
looks. A test asserts the queue is untouched and that the payload carries
a hint rather than an action.

An unreadable raw/ dir degrades to silence — brain_context is a hot path
and must not fail because the review queue is broken.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BeAp5LTscnz2W7Ubt4eJ6m

ingestion/internal/mcp/tools_context.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"time"
 
 	"github.com/mathiasbq/hyperguild/ingestion/internal/search"
 )
@@ -155,7 +156,14 @@ func (s *Server) brainContext(ctx context.Context, args json.RawMessage) (json.R
 		entries = entries[:limit]
 	}
 
-	return json.Marshal(map[string]any{"entries": entries})
+	out := map[string]any{"entries": entries}
+	// The queue nudge rides along with a call the session already makes, so
+	// noticing an aging note costs nobody a decision to go looking (#82).
+	// Advisory only, and absent entirely when there is nothing to say.
+	if n := pendingNudge(s.brainDir, time.Now(), pendingNudgeThreshold); n != nil {
+		out["pending_review"] = n
+	}
+	return json.Marshal(out)
 }
 
 // truncateExcerpt clamps an already-stripped excerpt to maxLen characters