feat: add blu-site static site generator and fix language issues

Build a complete static site generator in Lux that faithfully clones
blu.cx (elmstatic). Generates 14 post pages, section indexes, tag pages,
and a home page with snippets grid from markdown content.

Language fixes discovered during development:
- Add \{ and \} escape sequences in string literals (lexer)
- Register String.indexOf and String.lastIndexOf in type checker
- Fix formatter to preserve brace escapes in string literals
- Improve LSP hover to show documentation for let bindings and functions

ISSUES.md documents 15 Lux language limitations found during the project.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types.rs

@@ -1599,6 +1599,14 @@ impl TypeEnv {
                 "parseFloat".to_string(),
                 Type::function(vec![Type::String], Type::Option(Box::new(Type::Float))),
             ),
+            (
+                "indexOf".to_string(),
+                Type::function(vec![Type::String, Type::String], Type::Option(Box::new(Type::Int))),
+            ),
+            (
+                "lastIndexOf".to_string(),
+                Type::function(vec![Type::String, Type::String], Type::Option(Box::new(Type::Int))),
+            ),
         ]);
         env.bind("String", TypeScheme::mono(string_module_type));