feat(lang): L7 memory is safe unless it says unsafe

The typed buffers are slices: words/floats/fixeds/doubles/pointers(n) make
zeroed, bounds-checked []int/[]float/... and the type names mean them. buffer(n)
is a []byte, with text_of, Fs.read_bytes/write_bytes and view(xs, start, n).
bytes(), indexing a raw pointer or bytes, free, resize, Memory.*, raw file calls,
data_of and C externs are refused outside unsafe { } / unsafe function, and a
project's own files may write unsafe only with --unsafe; the runtime and packages
are the platform. A slice passed to an extern goes as its data.

What the change found: Sync's atomics on a slice header, words(n) uninitialised,
input's fixed axes in ints, truetype's fixed outlines as ints, skin matrices
typed int, gl_shader's source table made from raw bytes. render3d gets safe
entry points (safe_api.ludic). Rendering is byte-identical; a frame costs the same.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/ludic-cli/project.ludic

@@ -275,6 +275,7 @@ function parse_build_args(start: int) -> pointer {
     if a == "--headless" { g_mode = 2 }
     else if a == "--windowed" { g_mode = 1 }
     else if a == "--save-temps" { g_save = true }
+    else if a == "--unsafe" { g_unsafe_build = true }
     else if a == "-o" {
       ai += 1
       if ai < arg_count() { g_out = arg(ai) }