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>

selfhost/emit_head.ludic

@@ -102,6 +102,27 @@ fn emit_header() -> void {
   }
 }
 
+# One `declare <ret> @<sym>(<argtys>)` per `extern fn`, so the linker resolves the
+# call to the bound symbol. Emitted after the header; a program with no `extern fn`
+# emits nothing here, so un-networked builds stay byte-identical.
+fn emit_extern_decls() -> void {
+  var i = 0
+  while i < len(prog) {
+    let d = prog[i]
+    if d.kind == N_EXTERN {
+      emith("declare ");  emith(llty(d.ty));  emith(" @");  emith(d.a.s);  emith("(")
+      var f = 0
+      while f < len(d.kids) {
+        if f > 0 { emith(", ") }
+        emith(llty(d.kids[f].ty))
+        f = f + 1
+      }
+      emith(")\n")
+    }
+    i = i + 1
+  }
+}
+
 # The string runtime, emitted (once) into any program that uses `+`/`==`/`!=`
 # on strings. Hand-written IR over NUL-terminated byte buffers: str_eq walks both
 # until a mismatch or a shared terminator; str_concat measures both, mallocs