feat(compiler): list literals, typed compound assignment, file:line diagnostics

- `[a, b, c]` list literals (E_LIST → emit_list); static_type learns
  slice-element, `new T`, list, string and literal kinds
- `x op= y` lowers through the same path as `x = x op y` (emit_bin_vals):
  fixed `*=`/`/=` use the Q16.16 64-bit paths, string `+=` concatenates,
  int→long widens; unary `-` keeps a fixed operand's type (arith_ty)
- one `unescape()` table for "strings", 'chars' and `interpolation`;
  `'\''`, `'\\'`, `'\"'` no longer read as 0; unterminated char literals
  and unexpected characters are errors instead of silently skipped
- every diagnostic is `file:line: error: msg` (g_parse_file / g_err_file,
  Node.file + Node.line set by node()); tok_desc() in expectation errors;
  duplicate `function` names and unknown `phase` names are reported in
  source terms (phase_id used to default unknown phases to Overlay)
- interpolation holes skip braces inside string literals
- hand-IR preludes move from the user `@fn_` prefix to `@lp_` so a user
  `is_ws` / `str_eq` / `path_join` no longer collides at link time
- `@ClearColor(expr)` accepts any constant expression; `Os.pid()` added
  (docs page + inventory); `str_starts()` in support/str
- main.ludic: `else if` flag ladder, char literals, stale script comments
- examples/lang/operators.ludic covers all of the above; os.ludic covers
  Os.pid; docs pages for Os.pid and the Overlay phase; ten changesets
- reseeded: selfhost/ludicc.seed.ll is the new compiler's own fixpoint

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

selfhost/backend/game/emit_machine.ludic

@@ -37,7 +37,7 @@ function emit_machine(st: Node) -> void {
     s = emit_bind(`call i32 @fn_rt_reg(i32 {regv.code})`)
   }
   if nmach < len(mach_stk) { mach_stk[nmach] = st } else { push(mach_stk, st) }
-  nmach = nmach + 1
+  nmach += 1
   let endl = lbl("smend")
   var i = 0
   while i < len(st.kids) {
@@ -50,11 +50,11 @@ function emit_machine(st: Node) -> void {
     emit_block(state.a)
     if not g_term { emit("  br label %");  emit(endl);  emit("\n") }
     emit(nxt);  emit(":\n");  g_term = false
-    i = i + 1
+    i += 1
   }
   if not g_term { emit("  br label %");  emit(endl);  emit("\n") }
   emit(endl);  emit(":\n");  g_term = false
-  nmach = nmach - 1
+  nmach -= 1
 }
 
 # `become Name` — a machine state transition when Name is a state of an
@@ -66,7 +66,7 @@ function emit_become(st: Node) -> void {
     let m = mach_stk[nmach - 1]
     var target: Node = null
     var i = 0
-    while i < len(m.kids) { if (m.kids[i].s == st.s) { target = m.kids[i] };  i = i + 1 }
+    while i < len(m.kids) { if (m.kids[i].s == st.s) { target = m.kids[i] };  i += 1 }
     if (target != null) {
       let gv = machine_var(m.a)
       let sv = machine_state_value(m, target)