Create asset module and add origin configuration

Asset Module:
- Created internal/assets package for clean embedded static file management
- Embedded static files from single source location (static/ directory)
- Eliminated need for duplicate static files or symlinks
- Assets accessible via assets.Static from any package

Origin Configuration:
- Added origin field to configuration with latitude, longitude, and name
- Automatically calculates origin as average of source positions if not specified
- Displays origin information on startup
- Updated config.example.json to show origin usage

Architecture:
- Moved main.go back to cmd/skyview/ structure
- Updated Makefile to build from cmd/skyview
- Clean separation of concerns with reusable asset module

This provides a robust foundation for asset management and proper origin
handling for distance calculations and map centering.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

internal/assets/assets.go

@@ -0,0 +1,10 @@
+// Package assets provides embedded static web assets for the SkyView application.
+// This package embeds all files from the static/ directory at build time.
+package assets
+
+import "embed"
+
+// Static contains all embedded static assets
+// The files are accessed with paths like "static/index.html", "static/css/style.css", etc.
+//go:embed static/*
+var Static embed.FS