selfhost: fix parser infinite loop + lexer token limit

- Parser_Parse: add beforePos safeguard to skip unrecognized tokens
  instead of looping forever when parserParseDecl returns null
- Lexer: increase maxTokens 4096 -> 32768; add explicit break on limit
- CLI: null-check ReadFile result before String_Eq
- Nim CLI: add -O2 to cc invocation for faster self-hosted builds

_selfhost/src/parser.bux

@@ -1195,12 +1195,17 @@ func Parser_Parse(tokens: *LexToken, tokenCount: int) -> *Module {
             discard parserAdvance(p);
             continue;
         }
+        let beforePos: int = p.pos;
         let decl: *Decl = parserParseDecl(p);
         if decl != null as *Decl {
             decl.childDecl2 = mod.firstItem; // push front
             mod.firstItem = decl;
             mod.itemCount = mod.itemCount + 1;
         }
+        // Infinite-loop safeguard: if no progress, skip token
+        if p.pos == beforePos {
+            discard parserAdvance(p);
+        }
     }
 
     return mod;