Add mvnlog --web: local web server for interactive build report viewing

[gnodet]

Context

PR #12572 (Build Report Foundation) introduced mvnlog, a CLI tool that renders build reports as formatted terminal output. While the terminal output is functional, a web-based viewer would provide a much richer experience for exploring build reports.

Proposal

Add a --web flag to mvnlog that starts a lightweight local HTTP server serving an interactive build report viewer:

mvnlog --web              # starts on localhost, auto-opens browser
mvnlog --web --port 8080  # custom port

Implementation Plan

Server (Java — zero external dependencies)

Use the JDK built-in com.sun.net.httpserver.HttpServer (available since Java 6, no additional dependencies):

• / — serves a single HTML page with inlined CSS + vanilla JS (bundled as a classpath resource)
• /api/report — returns the raw build-report.json content
• /api/reports — lists available build reports
• Auto-open — java.awt.Desktop.browse(URI) to open the browser
• Self-terminating — shuts down after 30 minutes of inactivity, or Ctrl+C
• Port selection — try default port, fall back to random available port if busy

Frontend (single HTML file — no build step, no framework)

A single report.html resource bundled in the Maven distribution, containing:

Header

• Status badge (SUCCESS/FAILURE) with color
• Maven version, Java version, start time, total duration
• Goals executed, thread count

Module Timeline (Gantt chart)

• Horizontal bars showing parallel module builds
• Color-coded by status (green/red/gray)
• Hover for duration details
• Click to expand mojo breakdown

Mojo Detail Panel

• Click a module → see individual mojo executions
• Duration bars with proportional sizing
• Phase grouping (compile, test, package, etc.)
• Expandable log output per mojo

Problems Panel

• Filterable by severity (ERROR/WARN/INFO)
• Searchable by message text
• Each problem shows: key, source, suggestion (clickable), documentation URL (clickable link)
• Sortable by severity, source, key

Failures Panel

• Stack traces with syntax highlighting
• Module and mojo context
• Collapsible for long traces

Log Viewer

• Full build log with virtual scrolling (for large logs)
• Level-based filtering (ERROR/WARN/INFO/DEBUG)
• Module-scoped filtering
• Text search with highlighting

Design Principles

• No npm, no webpack, no React — vanilla HTML/CSS/JS only, bundled as a single file
• Responsive — works on mobile (check build status from phone)
• Dark/light mode — respects prefers-color-scheme
• Accessible — proper ARIA roles, keyboard navigation
• Offline — everything inlined, no CDN dependencies
• Small — target < 50KB for the HTML resource

Non-Goals (for this issue)

• Real-time streaming of ongoing builds (future enhancement)
• Multi-build comparison/history (future enhancement)
• Persistent server mode (future enhancement)
• Remote access / authentication (future enhancement)

Depends on

• Build Report Foundation — structured report, console modes, warning control #12572 (Build Report Foundation)