Networking N2–N6, and a fully C-free toolchain

Implement the rest of NETWORKING-DESIGN.md (N2–N6) and eliminate every
`.c` file from the repo. clang remains only the LLVM-IR assembler; no C
is compiled anywhere.

Networking (selfhost/emit_net.ludic + parser/emit changes):
- N2 @Sync: per-model serialize/apply + by-kind dispatchers; POD-scalar
  compile error and empty-participation warning; selective replication.
- N3 @Owned: @L_owner array + owner/set_owner/is_owner; owners snapshot.
- N4 @ToServer/@ToClients remote events: framed net_send + net_pump re-emit.
- N5 @Server/@Predicted role guards + drivable sim (tick_fixed/tick_render,
  entry-owns-the-loop).
- Built-in loopback transport so multiplayer runs with zero foreign code;
  extern fn net_send/net_poll still overrides it for a real socket.
- N6 blessed runtime (examples/net_rt.ludic) + end-to-end demo (net_demo).
- Fix: llty("entity") is now i32 (entities are i32 handles), so let e = self().

C elimination:
- Networking + foreign-mod-ABI tests rewritten as self-contained pure-Ludic
  programs (examples/net_*, world_*, mod_events, scoped); tests/ removed.
- Reflection ABI exposed to Ludic as world_* builtins (Ludic-to-Ludic modding).
- Formatter rewritten C→Ludic: tools/ludic-tools/fmt.ludic.
- Language server rewritten C→Ludic: tools/ludic-tools/lsp.ludic (lexer, index
  parser, cross-file workspace resolver, JSON, all LSP handlers).
- Obsolete migrate_*.c codemods deleted; ludic_syntax.h kept as vocabulary data.

Suites: ./test.sh 44/44, ./tools/test-tools.sh 28/28 (LSP 42/42), fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/net_echo.ludic

@@ -0,0 +1,24 @@
+# net_echo.ludic — N0: the transport seam (NETWORKING-DESIGN §5, §13 N0).
+#
+# The transport is two calls — net_send puts a datagram on the wire, net_poll
+# takes the next one off. A production build binds them to a real socket with
+# `extern fn net_send/net_poll` (UDP native, WebRTC/WebSocket wasm); absent that,
+# the compiler supplies a built-in in-process loopback, so a program is networked
+# end to end with NO foreign host — pure Ludic. This sends four bytes and polls
+# them back through the loopback: prints 4, then 10 20 30 42.
+program NetEcho {
+  entry {
+    let out = bytes(4)
+    out[0] = 10
+    out[1] = 20
+    out[2] = 30
+    out[3] = 42
+    net_send(0, out, 4)                  # onto the wire (the built-in loopback)
+
+    let inb = bytes(64)
+    let n = net_poll(inb, 64)            # take the next datagram back off
+    print(n)                             # 4
+    var i = 0
+    while i < n { print(inb[i]);  i = i + 1 }   # 10 20 30 42
+  }
+}