feat: Create VictoriaLogs HTTP Client (Issue #11)

- Create VictoriaLogs client package
- Implement Query method for LogsQL queries
- Implement StatsQuery for time-series stats
- Implement GetFacets for field facets
- Implement GetStreamIDs for stream identification
- Implement Tail for real-time log streaming
- Add Ingest method for testing
- Define all data models (LogEntry, QueryResult, etc.)
- Add comprehensive error handling

Closes #11

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/pkg/vlogs/models.go

@@ -0,0 +1,83 @@
+package vlogs
+
+import "time"
+
+// QueryParams represents parameters for a LogsQL query
+type QueryParams struct {
+	Query  string    `json:"query"`
+	Start  time.Time `json:"start,omitempty"`
+	End    time.Time `json:"end,omitempty"`
+	Limit  int       `json:"limit,omitempty"`
+	Offset int       `json:"offset,omitempty"`
+}
+
+// LogEntry represents a single log entry
+type LogEntry struct {
+	Timestamp time.Time              `json:"_time"`
+	StreamID  string                 `json:"_stream_id,omitempty"`
+	Message   string                 `json:"_msg"`
+	Fields    map[string]interface{} `json:"fields,omitempty"`
+}
+
+// QueryResult represents the result of a query
+type QueryResult struct {
+	Logs       []LogEntry `json:"logs"`
+	TotalCount int        `json:"total_count"`
+	Took       int        `json:"took_ms"`
+}
+
+// StatsParams represents parameters for a stats query
+type StatsParams struct {
+	Query string    `json:"query"`
+	Start time.Time `json:"start"`
+	End   time.Time `json:"end"`
+	Step  string    `json:"step,omitempty"` // e.g., "5m", "1h"
+}
+
+// StatsResult represents the result of a stats query
+type StatsResult struct {
+	Data []StatsDataPoint `json:"data"`
+}
+
+// StatsDataPoint represents a single data point in stats
+type StatsDataPoint struct {
+	Timestamp time.Time              `json:"timestamp"`
+	Values    map[string]interface{} `json:"values"`
+}
+
+// FacetsParams represents parameters for getting facets
+type FacetsParams struct {
+	Query string    `json:"query"`
+	Start time.Time `json:"start"`
+	End   time.Time `json:"end"`
+	Field string    `json:"field,omitempty"`
+}
+
+// FacetsResult represents the result of a facets query
+type FacetsResult struct {
+	Facets []Facet `json:"facets"`
+}
+
+// Facet represents a facet value with count
+type Facet struct {
+	Value string `json:"value"`
+	Count int    `json:"count"`
+}
+
+// StreamIDsParams represents parameters for getting stream IDs
+type StreamIDsParams struct {
+	Query string    `json:"query"`
+	Start time.Time `json:"start"`
+	End   time.Time `json:"end"`
+}
+
+// StreamIDsResult represents the result of stream IDs query
+type StreamIDsResult struct {
+	StreamIDs []string `json:"stream_ids"`
+}
+
+// TailParams represents parameters for tailing logs
+type TailParams struct {
+	Query string `json:"query"`
+	Limit int    `json:"limit,omitempty"`
+}