Improve agent-facing history endpoints (Phase 1)

- Fix /api/history/{type} to search the full persistent store instead of
  only the bounded in-memory ring buffer, so filtered history isn't
  silently truncated.
- Add structured type/since/until filters to /api/history/search and
  /api/history/wait, alongside the existing free-text query.
- Add GET /api/traces/{traceId} to fetch all entries for a trace in one
  call instead of relying on substring search.
- Rate-limit /api/history/wait per client IP.
- Add docs/PLAN.md tracking the phased improvement plan; update README
  and agents_example.md for the new/changed endpoints.

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

internal/storage/store.go

@@ -5,9 +5,24 @@ import (
 	"git.tornberg.me/go-otel/internal/websocket"
 )
 
+// SearchOptions narrows a Search call beyond the free-text query.
+type SearchOptions struct {
+	// Query is a case-insensitive substring match against the raw entry JSON.
+	Query string
+	// Type restricts results to a single telemetry type (traces, metrics, logs).
+	// Empty matches any type.
+	Type string
+	// Since restricts results to entries with Timestamp >= Since (unix nanoseconds).
+	// Zero means no lower bound.
+	Since int64
+	// Until restricts results to entries with Timestamp <= Until (unix nanoseconds).
+	// Zero means no upper bound.
+	Until int64
+}
+
 // Store interface for telemetry history persistence.
 type Store interface {
 	Append(ctx context.Context, entry websocket.HistoryEntry) error
 	GetHistory(ctx context.Context, limit int) ([]websocket.HistoryEntry, error)
-	Search(ctx context.Context, query string, limit int) ([]websocket.HistoryEntry, error)
+	Search(ctx context.Context, opts SearchOptions, limit int) ([]websocket.HistoryEntry, error)
 }