feat: REST API + Service Worker + diff viewer + MARC tool + enriched authority pages

Round 4 — five more high-impact additions.

1. Public REST API (the big reach multiplier)
   - /api/transliterate (GET + POST + OPTIONS) — real on-demand endpoint
     running interscript-ts server-side. No auth, no rate limits, CORS
     open. Returns {system, input, output, stage, durationMs}.
   - /api/systems — list/filter the catalogue (by authority, source_script,
     destination_script)
   - /api/detect — detection API endpoint (returns candidate systems
     for a given source-script family)
   - Added @astrojs/node adapter; output stays static for prerendered
     routes. API routes opt out via `export const prerender = false`.
   - 12 integration tests in test/api-endpoints.test.ts spawn the real
     server and curl each endpoint.

2. Service Worker for offline-first access
   - public/sw.js with stale-while-revalidate for HTML, cache-first for
     map IR + static assets, network-only for API
   - public/offline.html as the fallback with brand mark
   - Auto-registers from Base.astro (skips insecure origins)
   - After first visit, all 8MB of map IR is cached → site + worker +
     batch + compare all work without network. Critical for field
     researchers in low-bandwidth environments.

3. /diff — map rule-set comparison
   - Pick two systems, see their first 30 rules side-by-side
   - Each row shows kind (sub/parallel/run/funcall), from, →, to
   - Color-coded by kind (parallel=highlight, sub=brand, etc.)
   - Use cases: adoption decisions, map authoring, linguistic research

4. /marc — librarian MARC tool
   - Paste text-mode MARC fields (MarcEdit-style), get romanized 880
     parallel fields
   - Subfield-aware: only romanizes non-Latin content, leaves codes intact
   - ALA-LC systems preloaded (default for North American cataloging)
   - Privacy: text never leaves browser (Web Worker)
   - Links to LOC 880 reference

5. Enriched /authorities/[slug] pages
   - 11 narrative descriptions added for prominent authorities (BGN/PCGN,
     ISO, ALA-LC, ODNI, UN, ICAO, DIN, GOST, ELOT, MOFA, Academia Sinica, SAC)
   - Signature sample callout (dark ink panel) for prominent authorities
     showing a real test vector
   - Publication timeline by decade (visual bars)
   - Source script coverage with display names (via @iso24229/iso15924-data)

6. API playground updates
   - Hero now leads with the live curl snippet pointing at the real
     https://interscript.org/api/transliterate endpoint
   - Snippet URLs updated to match actual deployed path

Navigation: 13 → 16 destinations (added /diff, /marc).

Tests: 203 total (was 171).
- 12 new API integration tests (server spawned, real HTTP)
- 20 new round4 tests covering diff, marc, enriched authorities, SW
- All passing

Interscript-ts changes (companion):
- New `./loaders.node` subpath export so server-side code can import
  filesystemStrategy without pulling node:fs into browser bundles

Author: ronaldtse

astro.config.mjs

@@ -2,12 +2,16 @@
 import { defineConfig } from "astro/config"
 import vue from "@astrojs/vue"
 import tailwindcss from "@tailwindcss/vite"
+import node from "@astrojs/node"
 
 // Interscript.org v2 — Astro 7 + Vite 8 + Tailwind 4 + Vue 3 islands.
-// Uses interscript-ts for the map explorer.
+// Static output by default; per-route opt-out via `export const prerender = false`.
+// The /api/* endpoints are real on-demand Node routes served via
+// @astrojs/node. Deploy target: any Node-capable host.
 export default defineConfig({
   site: "https://www.interscript.org",
   output: "static",
+  adapter: node({ mode: "standalone" }),
   integrations: [vue()],
   vite: {
     plugins: [tailwindcss()],