refactor(core): optimize performance, fix concurrency and clean up AGENTS.md design violations

- Concurrency: Added lock protection to WebSocket writes, fixed timer leaks, and prevented config cache listener context leaks.
- Performance: Added memory cache in ObservabilityBufferStore, periodic cleaning in CH Deduplicator, and buffered ZIP batch download writes.
- Design: Introduced Redis caching for OAuth session/tokens, sanitized raw DB error messages, segregated handlers and logics, and standard CAP response envelopes.

pkg/wsclient/client.go

@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+	"sync"
 	"time"
 
 	"golang.org/x/net/websocket"
@@ -52,6 +53,7 @@ type Connection struct {
 	Conn        *websocket.Conn
 	URL         string
 	ReadTimeout time.Duration
+	writeMu     sync.Mutex
 }
 
 // New creates a new WebSocket client with the given configuration.
@@ -154,6 +156,9 @@ func (conn *Connection) SendMessage(msgType string, payload any) error {
 		Payload: payload,
 	}
 
+	conn.writeMu.Lock()
+	defer conn.writeMu.Unlock()
+
 	_ = conn.Conn.SetWriteDeadline(time.Now().Add(writeDeadlineSecs * time.Second))
 	return websocket.JSON.Send(conn.Conn, message)
 }