Fix VPN routing/DNS, ping latency display, and add user portal

[Copilot]

Users reported that VPN connections showed as established but no sites loaded, config selection showed misleading 0ms pings as "fastest", and there was no self-service portal for clients to access their configs.

Server — V2Ray client config (server/protocols/v2ray.py)

• Added dns block (8.8.8.8, 1.1.1.1, 8.8.4.4) to generated client Xray config — previously absent, causing DNS failures through the tunnel
• Replaced geosite:cn/geoip:cn routing rules with explicit RFC-1918 CIDR bypass; geo-data files are not bundled with the Windows client, making these rules silently inert
• Changed domainStrategy from AsIs → IPIfNonMatch

# Before — fails silently without geo files on client
"routing": {
    "domainStrategy": "AsIs",
    "rules": [
        {"type": "field", "outboundTag": "direct", "domain": ["geosite:cn", "geosite:private"]},
        {"type": "field", "outboundTag": "direct", "ip": ["geoip:cn", "geoip:private"]}
    ]
}

# After — works everywhere, no file dependencies
"dns": {"servers": ["8.8.8.8", "1.1.1.1", "8.8.4.4"]},
"routing": {
    "domainStrategy": "IPIfNonMatch",
    "rules": [{"type": "field", "outboundTag": "direct",
               "ip": ["127.0.0.0/8", "10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16"]}]
}

Server — Missing logger (server/routes/panel_api.py)

• Added import logging and logger = logging.getLogger(...) — was causing NameError crashes on core start/stop/restart error paths.

Client — Ping accuracy (client/services/api.ts, client/components/ProfilesPage.tsx)

• PingAllProfiles previously called /ping-all which returned latency: 0 for every running protocol (server only checks process state, not connectivity). Replaced with parallel real ICMP pings via the native measure_latency Tauri command.
• Sort, display badges, stats counter, and auto-pilot selection now treat latency === 0 as unmeasured rather than "fastest". Only latency > 0 results participate in ranking.

Web Panel — User portal (web-panel/pages/UserPortalPage.tsx, web-panel/App.tsx, web-panel/components/Sidebar.tsx)

New self-service portal at /candyconnect/user — no admin credentials required. Uses existing /client-api endpoints.

Features:

• Client login (username + password)
• Account dashboard: traffic usage progress bar, expiry date, last connection IP
• Per-config actions: copy VLESS/VMess/Trojan links, download WireGuard .conf, download OpenVPN .ovpn, display L2TP/IKEv2 server+credentials
• Admin sidebar gains a "User Portal" external link for easy sharing with end users

Portal is activated by path detection (window.location.pathname.includes('/user')); the existing SPA catch-all in server/main.py already serves index.html for all /candyconnect/* paths.

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