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/tests/datetime.ludic

@@ -2,7 +2,7 @@ program T {
   entry {
     # Duration — spans in whole seconds
     print(Duration.hours(3))                          # 10800
-    print(Duration.minutes(5) + Duration.seconds(30)) # 330
+    print(Duration.minutes(5) + Duration.seconds(30))  # 330
     print(Duration.days(2))                           # 172800
     print(Duration.as_hours(10800))                   # 3
     print(Duration.as_days(172800))                   # 2
@@ -25,7 +25,7 @@ program T {
     let feb = Date.add_days(Date.new(2026, 1, 1), 31)
     print(Date.month(feb))                            # 2
     print(Date.day(feb))                              # 1
-    print(Date.diff_days(Date.new(2026, 1, 1), Date.new(2025, 1, 1))) # 365
+    print(Date.diff_days(Date.new(2026, 1, 1), Date.new(2025, 1, 1)))  # 365
 
     # DateTime — instant as seconds-since-1970
     let t = DateTime.from(2000, 1, 1, 12, 30, 15)
@@ -38,6 +38,6 @@ program T {
     print(DateTime.second(t))                         # 15
     print(DateTime.weekday(t))                        # 6
     print(DateTime.date(t))                           # 10957
-    print(DateTime.hour(DateTime.add(0, Duration.hours(1)))) # 1
+    print(DateTime.hour(DateTime.add(0, Duration.hours(1))))  # 1
   }
 }