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>

docs/language/builtins/fn-ui_build.md

@@ -24,19 +24,19 @@ program TitleMenu {
   }
 
   handler Boot phase Start {
-    title_font = font_load("/System/Library/Fonts/Supplemental/Arial.ttf")
+    title_font = Font.load("/System/Library/Fonts/Supplemental/Arial.ttf")
     ui_build()
-    ui_open(UI_MainMenu)
+    Ui.open(UI_MainMenu)
   }
 
   handler Navigate phase Update {
-    ui_tick(Input.key())
-    if ui_clicked(UI_Quit) { quit() }
+    Ui.tick(Input.key())
+    if Ui.clicked(UI_Quit) { quit() }
   }
 
   handler DrawWorld phase Render {
     Screen.clear(Color.MidnightBlue)
-    ui_render()
+    Ui.render()
     Screen.show()
   }
 }