v2: Refactor to graph-based dependency injection with modular node architecture

Summary

This is a major refactor that introduces graft as a dependency injection framework, restructuring the server into composable, dependency-aware nodes. The v1 pattern remains available via the v1 branch/tag for users who prefer a simpler, non-DI approach.

Changes

Architecture

• New pkg/nodes/ package - Modular node-based architecture replacing the monolithic pkg/server/:
  • config/ - Environment configuration as a cacheable graft node
  • router/ - Echo router setup with middleware and route registration
  • server/ - HTTP server with explicit dependencies on config and router nodes
• Deleted pkg/server/ - Replaced by the nodes architecture

Bootstrap

• Simplified cmd/main.go using graft.ExecuteFor[server.Output]() to bootstrap the entire dependency graph
• Cleaner signal handling and graceful shutdown

Auth & Error Handling

• New web/pages/authfail/ - Dedicated unauthorized page template
• Enhanced error handler renders the authfail page for 401 responses
• Auth middleware demonstrates rejection flow with ?username=reject

Dependencies

• Added github.com/grindlemire/graft for dependency injection

Breaking Changes

The internal structure is significantly different from v1. If you've built on top of v1:

• pkg/server/ no longer exists - migrate to pkg/nodes/ pattern
• Server bootstrap now uses graft's node execution model

Migration

For users who prefer the simpler v1 pattern without DI:
git clone --branch v1 https://github.com/grindlemire/gothem-stack.git