Finch 2.4.0: methods, maps, errors as values; str() of any value; macOS and ARM64 docs; Kate support

- fn Struct.method(...) with self by reference, also on C structs
- map[K]V: insertion-ordered hash maps, literals, m[k] += 1, has/get/remove/keys/values
- -> T! / -> !, return error(...), or <value>, or { err }, try; fallible int/float/read_file/write_file/delete_file
- for i, x in list / for k, v in map
- print and str() share one text formatter
- LSP: method and map completion, method signatures; grammar and snippets for VS Code and Kate
- tests: 74 (methods, errors, maps + 11 failure cases); docs at all three levels, en and pl

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

tests/fail/method_loop_readonly.fch

@@ -0,0 +1,12 @@
+// expect: the loop variable 'c' can't be changed
+struct Counter {
+    int n
+}
+fn Counter.bump() {
+    self.n += 1
+}
+fn main() {
+    for c in [Counter(1), Counter(2)] {
+        c.bump()
+    }
+}