feat(receiver): storage layer and webhook payload compat

Dual-dialect store (SQLite via modernc.org, MySQL via go-sql-driver,
both pure Go) with order-tolerant start/complete upserts, filtered and
paginated listing, and aggregate queries (per-day, top domains, query
types, statuses, duration percentiles, top clients). Sender gains
optional EXPLOREDNS_WEBHOOK_TOKEN bearer auth; a round-trip test pins
receiver structs byte-compatible with the sender payloads.

Note: go directive moves to 1.25.0, required by modernc.org/sqlite.
CI reads the version from go.mod so GOTOOLCHAIN=local stays satisfied.

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

internal/receiver/store/events.go

@@ -0,0 +1,39 @@
+package store
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// StartEvent and CompleteEvent are the receiver-side decodings of the
+// webhook payloads posted by the main app. Field names and JSON tags must
+// stay in sync with webhookStartEvent/webhookCompleteEvent in
+// web/api/webhook.go; a compatibility test in web/api enforces this.
+
+// StartEvent mirrors web/api webhookStartEvent.
+type StartEvent struct {
+	Event     string    `json:"event"`
+	ID        string    `json:"id"`
+	Domain    string    `json:"domain"`
+	QueryType string    `json:"query_type"`
+	AllRoots  bool      `json:"all_roots"`
+	ClientIP  string    `json:"client_ip"`
+	StartedAt time.Time `json:"started_at"`
+}
+
+// CompleteEvent mirrors web/api webhookCompleteEvent. Summary is kept as
+// raw JSON: the receiver stores it verbatim and never interprets it.
+type CompleteEvent struct {
+	Event       string          `json:"event"`
+	ID          string          `json:"id"`
+	Domain      string          `json:"domain"`
+	QueryType   string          `json:"query_type"`
+	ClientIP    string          `json:"client_ip"`
+	StartedAt   time.Time       `json:"started_at"`
+	DoneAt      time.Time       `json:"done_at"`
+	DurationMS  int64           `json:"duration_ms"`
+	Status      string          `json:"status"`
+	Error       string          `json:"error,omitempty"`
+	ResultCount int             `json:"result_count"`
+	Summary     json.RawMessage `json:"summary"`
+}