docs: comprehensive documentation expansion

Add 4 new doc files (configuration reference, development guide, API
reference with full request/response schemas, database schema), expand
the README with a feature list and how-it-works walkthrough, fix
missing Firmware and Burn stages in architecture.md and test-suite.md,
add threshold engine and host-mode agent sections, and add godoc
comments to 11 packages and 6 model types.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/web/embed.go

@@ -1,3 +1,5 @@
+// Package web embeds the static assets (CSS, JS) and compiled Templ
+// templates served by the orchestrator's HTTP routes.
 package web
 
 import "embed"