Extract KVM UI assets and replace alert() with status banner

[nesvet]

Summary

Fixes server UI issues without changing the WebSocket protocol: invalid inline CSS, alert() for notices, logout not clearing cookies, fragile connect DOM replacement, and missing context for multi-host deployments.

Changes

• main.py — version=__version__ for cache busting; server_labels for multi-host display
• static/app.core.css, static/app.core.js — extracted core UI behaviour
• templates/base.tpl, templates/index.tpl, templates/index_instant.tpl
• templates/_resolution_select.tpl, templates/_server_field.tpl, templates/_session_log.tpl
• Status banner and session log instead of alert()
• Connect form stays in the DOM; noVNC iframe created via DOM APIs
• Logout calls cookie cleanup

Test plan

• Wrong password → message in banner, form still usable
• Successful connect → noVNC iframe, session log entries
• Logout clears auth cookies
• Hard refresh loads new static assets via version query param

Tested on ASUS ASMB8-iKVM firmware 1.14.2: single-host connect, error notice in banner, labels shown when server_labels configured.

Closes #8

[nesvet]

server_labels on a single-host config; notice text duplicated in banner and session log.