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/stdlib/emit_ease.ludic

@@ -65,10 +65,10 @@ function ease_eval(mode: int, t: pointer) -> pointer {
     g_uses_mathrt = true                            # 2^(-10t) * sin((10t - 0.75) * 2pi/3) + 1
     let tt = emit_bind(`mul i32 {t}, 10`)            # 10t
     let ntt = emit_bind(`sub i32 0, {tt}`)           # -10t (exp2 exponent, Q16.16)
-    let decay = emit_bind(`call i32 @fn_fx_exp2(i32 {ntt})`)
+    let decay = emit_bind(`call i32 @lp_fx_exp2(i32 {ntt})`)
     let ph = emit_bind(`sub i32 {tt}, 49152`)        # 10t - 0.75
     let ang = fx_mul_code(ph, "137258")              # * (2pi/3), 2pi/3 = 137258 fixed
-    let s = emit_bind(`call i32 @fn_fx_sin(i32 {ang})`)
+    let s = emit_bind(`call i32 @lp_fx_sin(i32 {ang})`)
     let osc = fx_mul_code(decay, s)
     return emit_bind(`add i32 {osc}, 65536`)
   }
@@ -82,6 +82,6 @@ function emit_ease_ns(meth: pointer, e: Node) -> Val {
   if (meth == "out")    { return val(ease_eval(2, t.code), "fixed") }
   if (meth == "in_out") { return val(ease_eval(3, t.code), "fixed") }
   if (meth == "back")   { return val(ease_eval(4, t.code), "fixed") }
-  if (meth == "elastic"){ return val(ease_eval(5, t.code), "fixed") }
+  if (meth == "elastic") { return val(ease_eval(5, t.code), "fixed") }
   return val(ease_eval(6, t.code), "fixed")         # bounce
 }