Add code health lint guards, consolidate relay constants, document agent prompts

Three CI-enforced lint scripts to prevent common codebase growth problems:

- lint:file-size — enforces 1000-line max for new JS files, grandfathers
  existing oversized files and prevents them from growing further
- lint:innerhtml — tracks innerHTML usage per-file with a baseline count,
  blocks new innerHTML additions (guides agents toward safe DOM APIs)
- Relay constants consolidated from duplicate definitions in client.js and
  ConnectionManager.js into shared js/nostr/relayConstants.js
- AGENTS.md Section 13: documents all three rules with examples
- docs/scheduled-agent-prompts.md: copy-paste prompts for recurring
  file decomposition, innerHTML migration, and constant dedup tasks

https://claude.ai/code/session_01LzErpH9FNw4hAPsjoYb1v9

package.json

@@ -16,7 +16,9 @@
     "ci:beacon": "npm run build:beacon",
     "format": "prettier --cache --write css/tailwind.source.css css/tokens.css css/docs.css \"docs/**/*.html\" tailwind.config.cjs README.md CONTRIBUTING.md",
     "audit": "node scripts/daily-design-system-audit.mjs",
-    "lint": "npm run lint:css && npm run lint:hex && npm run lint:inline-styles && npm run lint:tokens && npm run lint:tailwind-brackets && npm run lint:tailwind-colors",
+    "lint": "npm run lint:css && npm run lint:hex && npm run lint:inline-styles && npm run lint:tokens && npm run lint:tailwind-brackets && npm run lint:tailwind-colors && npm run lint:file-size && npm run lint:innerhtml",
+    "lint:file-size": "node scripts/check-file-size.mjs",
+    "lint:innerhtml": "node scripts/check-innerhtml.mjs",
     "lint:css": "stylelint css/tailwind.source.css css/tokens.css css/docs.css",
     "lint:hex": "node scripts/check-hex.js",
     "lint:inline-styles": "node scripts/check-inline-styles.mjs",