Restructure AGENTS.md into scoped guides

Trim AGENTS.md to whole-repo, every-session facts (154 -> 110 lines) and move
subsystem guidance into docs/guides/*.md, each with paths: frontmatter and a
one-line index entry in AGENTS.md. Symlink each guide from .claude/rules/ so
Claude Code lazy-loads it by matching path; track those symlinks via a
.gitignore exception (.claude/settings.local.json stays ignored).

docs/guides/admin-ui.md

@@ -0,0 +1,25 @@
+---
+paths:
+  - "licensing-service-startos/licensing-service/web/**"
+  - "licensing-service-startos/licensing-service/src/api/admin_ui.rs"
+---
+
+# Admin SPA conventions (web/index.html)
+
+The admin UI is a single embedded `web/index.html` (rust-embed), served via
+`api/admin_ui.rs`.
+
+## Pill / toggle colors
+
+- **Navy-filled** — selected / on state.
+- **Cream-outlined** — off state.
+- **Opacity** (not strikethrough) — muted / disabled.
+- **Gold** is reserved **strictly for marketing accents** (most-popular badge,
+  launch-special ribbon). Never use gold for ordinary selected/on state.
+
+## Reference flows
+
+- `openBtcpayConnectModal` is the reference implementation for the BTCPay
+  one-click connect flow — see [payments](payments.md).
+
+Don't rewrite user-facing copy in here outside the explicit scope of a request.