Harden network and privacy defaults; fix several bugs

Security:
- Bind HTTP gateway to 127.0.0.1 by default; add --bind for LAN opt-in
- Restrict Reticulum mesh surface to GET /api/sites only (CSRF cannot
  authenticate mesh callers, so gate by whitelist)
- Cap request body size at 16 MiB to prevent memory DoS
- Redact /bookmark query strings from request logs so the bookmark token
  and URLs do not land in stdout / docker / journal logs
- Tighten FTS5 sanitizer: strip colon, drop AND/OR/NOT/NEAR operator words
- Expand .dockerignore; document trust model in README

Features:
- Add sharing mode toggle (share everything except private vs share only
  public-tagged) with /share/preview so users can see what subscribers
  would receive before enabling sharing

Bugs:
- handle_export() crashed on every call (missing query kwarg)
- Dead float16 decompression branch in embeddings.py silently corrupted
  the HNSW index when compress_embeddings was on
- GATEWAY_PORT staleness: --port and find_available_port had no effect
  on the actual bind
- semantic_search default mismatched between db.py ("1") and the rest of
  the app ("0"), causing embeddings to be generated when the UI said off
- Connection pool returned connections with uncommitted transactions to
  the next consumer
- Gateway POST body decode 502'd on non-UTF-8 input
- ensure_rns_config clobbered user-edited ~/.reticulum/config; now only
  rewrites files it authored (sentinel-tagged)

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

gateway.py

@@ -1,3 +1,4 @@
+import re
 import sys
 import time
 import threading
@@ -9,6 +10,7 @@ APP_NAME = "tinyweb"
 ASPECTS = ["server"]
 GATEWAY_PORT = 8080
 REQUEST_TIMEOUT = 60
+MAX_BODY_SIZE = 16 * 1024 * 1024  # 16 MiB — covers /import and every other form
 
 
 class GatewayState:
@@ -71,8 +73,18 @@ class GatewayHandler(BaseHTTPRequestHandler):
 
         body = {}
         if method == "POST":
-            length = int(self.headers.get("Content-Length", 0))
-            raw = self.rfile.read(length).decode()
+            try:
+                length = int(self.headers.get("Content-Length", 0))
+            except ValueError:
+                self.send_error(400, "Invalid Content-Length")
+                return
+            if length < 0:
+                self.send_error(400, "Invalid Content-Length")
+                return
+            if length > MAX_BODY_SIZE:
+                self.send_error(413, "Request body too large")
+                return
+            raw = self.rfile.read(length).decode("utf-8", errors="replace")
             body = parse_qs(raw)
 
         # Parse cookies
@@ -152,7 +164,14 @@ class GatewayHandler(BaseHTTPRequestHandler):
         self._forward("POST")
 
     def log_message(self, format, *args):
-        print(f"[Gateway] {args[0]}")
+        try:
+            msg = format % args
+        except TypeError:
+            msg = format
+        # /bookmark carries a long-lived token and the URL being indexed —
+        # redact the query so it doesn't end up in stdout, journald, docker logs, etc.
+        msg = re.sub(r'(/bookmark)\?\S*', r'\1?[redacted]', msg)
+        print(f"[Gateway] {msg}")
 
 
 def main():