fix: v1.9.6 — Code.gs/CodeFull.gs hardening, goog.script.init unwrap, README rewrite

Server-side (Apps Script) fixes — users replace their Code.gs with assets/apps_script/Code.gs (or CodeFull.gs for full mode) and Manage deployments → ✏️ → New version → Deploy:
- Removed duplicate doGet in Code.gs (HtmlService one was overriding ContentService one due to JS hoisting → every GET to /exec returned a goog.script.init iframe instead of the placeholder HTML)
- CodeFull.gs doGet switched from HtmlService to ContentService (same reason)
- SKIP_HEADERS now strips X-Forwarded-* / Forwarded / Via family — second line of defense to v1.2.9's client-side stripping (#104), in case a misconfigured upstream proxy adds these
- _doBatch fallback when UrlFetchApp.fetchAll() throws as a whole — per-item fetch on safe methods so one bad URL no longer poisons the entire batch (port from masterking32@3094288)

Client-side (Rust) defense-in-depth:
- parse_relay_json now unwraps goog.script.init("...userHtml...") if any deployment returns the iframe-wrapped form (legacy Code.gs, or a redirect that GETs doGet). New extract_apps_script_user_html + decode_js_string_escapes helpers. Tested against a real deployment's doGet response.

Docs:
- README rewritten as short bilingual landing page (English + Persian RTL) targeting normal users; advanced reference moved to docs/guide.md + docs/guide.fa.md.

Tests: 3 new regression tests. 176 lib + 33 tunnel-node tests passing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -2222,7 +2222,7 @@ dependencies = [
 
 [[package]]
 name = "mhrv-rs"
-version = "1.9.5"
+version = "1.9.6"
 dependencies = [
  "base64 0.22.1",
  "bytes",