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/detach.ludic

@@ -0,0 +1,38 @@
+# detach.ludic — the structural attach/detach pair and its @OnAttach / @OnDetach
+# hooks. `attach P on e` adds a property to a LIVE entity (seeding its fields and
+# firing @OnAttach); `detach P on e` removes it (firing @OnDetach, which still
+# reads the outgoing value before the has-flag clears). This is the structural
+# counterpart to enable/disable — attach/detach create and destroy the property's
+# presence, whereas disable/enable only pause it while keeping the data.
+#
+# Running it prints: 15 1 25 0
+#   15   @OnAttach(Shield): amount seeded to 5, prints 5 + 10
+#   1    one live Shield now matches the query
+#   25   @OnDetach(Shield): reads the outgoing amount 5, prints 5 + 20
+#   0    the Shield is gone — nothing matches
+#
+#   ./selfhost/game-build.sh build/ludicc examples/detach.ludic /tmp/detach
+#   /tmp/detach </dev/null
+program Detach {
+  property Tag    { v: int = 0 }
+  property Shield { amount: int = 0 }
+  model Unit { Tag }
+
+  @OnAttach(Shield) handler Up   { print(Shield.amount + 10) }   # structural: property born
+  @OnDetach(Shield) handler Down { print(Shield.amount + 20) }   # structural: property dies
+
+  handler Seed phase Start { spawn Unit { Tag { v: 1 } } }
+
+  handler Run phase Render {
+    for (u) in query [Unit] { attach Shield on self() { amount: 5 } }   # @OnAttach -> 15
+    var n = 0
+    for (s) in query [Shield] { n += 1 }
+    print(n)                                                           # 1
+
+    for (s) in query [Shield] { detach Shield on self() }              # @OnDetach -> 25
+    n = 0
+    for (s) in query [Shield] { n += 1 }
+    print(n)                                                           # 0
+    quit()
+  }
+}