feat(stats): resource metrics dashboard + sites logs/stats

Background collector samples CPU/memory/network/block I/O for every
instance and site on a configurable interval (default 15s, range
5-300s), persists samples to SQLite with a configurable retention
window (default 2h, range 0-24h), and skips ticks gracefully when
the Docker daemon is unreachable. Settings are reloadable without
a restart — each tick re-reads them.

New API endpoints:
- GET /api/system/stats (host snapshot: info + df)
- GET /api/system/stats/history
- GET /api/system/stats/top?by=cpu|memory
- GET /api/projects/{id}/stages/{s}/instances/{iid}/stats/history
- GET /api/sites/{id}/stats[/history]
- GET /api/sites/{id}/logs (SSE + JSON, reuses instance log streamer)

Frontend:
- ECharts added with tree-shaken imports (~180KB gzip) for
  future-proof time-series/gantt/graph visualizations
- CollapsibleSection wraps all dashboard sections (system health,
  daemons, system resources, static sites, projects) with
  localStorage-persisted open state
- SystemResourcesCard shows capacity tiles, workload utilization
  chart with 30m/2h/6h/24h window picker, disk breakdown with
  reclaimable callouts, and top 5 consumers
- ContainerStats and ContainerLogs take a source discriminated union
  so sites reuse the same components as instances; sites detail page
  embeds both for Deno backend debugging
- Settings › Maintenance exposes collection interval + retention
- Docker-unavailable state returns 503 and renders an amber banner
  instead of a generic 500

Full i18n coverage (en + ru) for all new strings.

internal/docker/stats.go

@@ -4,21 +4,30 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"strings"
+	"time"
 
 	"github.com/moby/moby/api/types/container"
 	"github.com/moby/moby/client"
 )
 
-// ContainerStats holds computed CPU and memory usage for a container.
+// ContainerStats holds computed CPU, memory, network, and block I/O
+// usage for a container. Network and block I/O values are cumulative
+// byte counters — compute rates by differencing two samples.
 type ContainerStats struct {
-	CPUPercent    float64 `json:"cpu_percent"`
-	MemoryUsage  int64   `json:"memory_usage"`
-	MemoryLimit  int64   `json:"memory_limit"`
-	MemoryPercent float64 `json:"memory_percent"`
+	Timestamp       time.Time `json:"timestamp"`
+	CPUPercent      float64   `json:"cpu_percent"`
+	MemoryUsage     int64     `json:"memory_usage"`
+	MemoryLimit     int64     `json:"memory_limit"`
+	MemoryPercent   float64   `json:"memory_percent"`
+	NetworkRxBytes  int64     `json:"network_rx_bytes"`
+	NetworkTxBytes  int64     `json:"network_tx_bytes"`
+	BlockReadBytes  int64     `json:"block_read_bytes"`
+	BlockWriteBytes int64     `json:"block_write_bytes"`
 }
 
 // GetContainerStats retrieves a one-shot stats snapshot for the given container
-// and computes CPU and memory percentages.
+// and computes CPU, memory, network, and block I/O metrics.
 func (c *Client) GetContainerStats(ctx context.Context, containerID string) (ContainerStats, error) {
 	result, err := c.api.ContainerStats(ctx, containerID, client.ContainerStatsOptions{
 		Stream:                false,
@@ -42,14 +51,53 @@ func (c *Client) GetContainerStats(ctx context.Context, containerID string) (Con
 		memPercent = float64(memUsage) / float64(memLimit) * 100.0
 	}
 
+	rxBytes, txBytes := sumNetworkBytes(stats.Networks)
+	readBytes, writeBytes := sumBlockIOBytes(stats.BlkioStats.IoServiceBytesRecursive)
+
+	ts := stats.Read
+	if ts.IsZero() {
+		ts = time.Now().UTC()
+	}
+
 	return ContainerStats{
-		CPUPercent:    cpuPercent,
-		MemoryUsage:  memUsage,
-		MemoryLimit:  memLimit,
-		MemoryPercent: memPercent,
+		Timestamp:       ts,
+		CPUPercent:      cpuPercent,
+		MemoryUsage:     memUsage,
+		MemoryLimit:     memLimit,
+		MemoryPercent:   memPercent,
+		NetworkRxBytes:  rxBytes,
+		NetworkTxBytes:  txBytes,
+		BlockReadBytes:  readBytes,
+		BlockWriteBytes: writeBytes,
 	}, nil
 }
 
+// sumNetworkBytes aggregates rx/tx byte counters across all network interfaces
+// for a single container. Missing Networks map (disabled networking) yields zeros.
+func sumNetworkBytes(nets map[string]container.NetworkStats) (rx, tx int64) {
+	for _, n := range nets {
+		rx += int64(n.RxBytes)
+		tx += int64(n.TxBytes)
+	}
+	return rx, tx
+}
+
+// sumBlockIOBytes totals read/write bytes across all block devices from the
+// cgroup io_service_bytes_recursive entries. The "Op" field is "read"/"write"
+// on cgroup v2 and "Read"/"Write" on cgroup v1 — match case-insensitively so
+// either runtime works.
+func sumBlockIOBytes(entries []container.BlkioStatEntry) (read, write int64) {
+	for _, e := range entries {
+		switch {
+		case strings.EqualFold(e.Op, "read"):
+			read += int64(e.Value)
+		case strings.EqualFold(e.Op, "write"):
+			write += int64(e.Value)
+		}
+	}
+	return read, write
+}
+
 // calculateCPUPercent computes CPU usage percentage from a stats response
 // using the delta between current and previous CPU readings.
 func calculateCPUPercent(stats container.StatsResponse) float64 {