Structs, arrays, owned strings, memory model, modules, debug info

- struct with default values; constructors Point(1, 2) / Point(x: 1); field access, auto-deref through pointers
- []T arrays with bounds checks, literals, for-each, push/pop/insert/remove/clear/resize/find/contains/join/slice/reverse/sort
- str carries its length: .len, s[i], +, comparison, sub/find/split/trim/upper/lower/replace/repeat/bytes, str(x), int(s), float(s)
- Memory: values own their memory and are freed at the end of their block; assignment copies, temporaries move;
  parameters are lent and only copied when the function changes them; defer; new()/free() for manual heap memory
- input(), read_file/write_file/file_exists, exit(), fn main([]str args)
- Finch modules: import name, module.fn(), module.Struct
- C structs from headers (fields, fixed arrays, nested); passed and returned by value with the System V x86-64 ABI;
  addr(fn) gives C a callback
- link "file.c" compiles and links your own C code
- -g emits DWARF debug info (gdb/lldb)
- Small C runtime (runtime/finch_rt.c) embedded in the compiler, cached in ~/.cache/finch
- Tests: 58, all clean under valgrind (MEMCHECK=1 tests/run.sh)

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

src/lexer.h

@@ -8,10 +8,10 @@ enum class Tok {
     Ident, Int, Float, String, Char,
 
     // keywords
-    Fn, Return, If, Else, While, For, In, Break, Continue, True, False, Null, Import, Link,
+    Fn, Return, If, Else, While, For, In, Break, Continue, True, False, Null, Import, Link, Struct, Defer,
 
     // punctuation
-    LParen, RParen, LBrace, RBrace, LBracket, RBracket, Comma, Dot, DotDot, Arrow,
+    LParen, RParen, LBrace, RBrace, LBracket, RBracket, Comma, Colon, Dot, DotDot, Arrow,
 
     // operators
     Plus, Minus, Star, Slash, Percent,
@@ -30,5 +30,6 @@ struct Token {
     bool newlineBefore;  // token starts a new line: ends the previous statement
 };
 
-std::vector<Token> lex(const std::string &src, const std::string &file);
+// Lexes g_files[file].text.
+std::vector<Token> lex(int file);
 const char *tokName(Tok t);