fix: C backend String functions, record type aliases, docs cleanup

- Add String.fromChar, chars, substring, toUpper, toLower, replace,
  startsWith, endsWith, join to C backend
- Fix record type alias unification by adding expand_type_alias and
  unify_with_env functions
- Update docs to reflect current implementation status
- Clean up outdated roadmap items and fix inconsistencies
- Add comprehensive language comparison document

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/README.md

@@ -153,27 +153,26 @@ A sequential guide to learning Lux, from basics to advanced topics.
 8. [Error Handling](guide/08-errors.md) - Fail effect, Option, Result
 9. [Standard Library](guide/09-stdlib.md) - Built-in functions
 10. [Advanced Topics](guide/10-advanced.md) - Traits, generics, optimization
+11. [Databases](guide/11-databases.md) - SQL, transactions, testing with handlers
 
 ### [Language Reference](reference/syntax.md)
 Complete syntax and semantics reference.
 
 - [Syntax](reference/syntax.md) - Grammar and syntax rules
-- [Types](reference/types.md) - Type system details
-- [Effects](reference/effects.md) - Effect system reference
-- [Standard Library](reference/stdlib.md) - All built-in functions
+- [Standard Library](guide/09-stdlib.md) - Built-in functions and modules
 
 ### [Tutorials](tutorials/README.md)
 Project-based learning.
 
-**Standard Programs:**
 - [Calculator](tutorials/calculator.md) - Basic REPL calculator
-- [Todo App](tutorials/todo.md) - File I/O and data structures
-- [HTTP Client](tutorials/http-client.md) - Fetching web data
-
-**Effect Showcases:**
 - [Dependency Injection](tutorials/dependency-injection.md) - Testing with effects
-- [State Machines](tutorials/state-machines.md) - Modeling state with effects
-- [Parser Combinators](tutorials/parsers.md) - Effects for backtracking
+- [Project Ideas](tutorials/project-ideas.md) - Ideas for building with Lux
+
+### Design Documents
+- [Packages](PACKAGES.md) - Package manager and dependencies
+- [SQL Design Analysis](SQL_DESIGN_ANALYSIS.md) - SQL as built-in vs package
+- [Roadmap](ROADMAP.md) - Development priorities and status
+- [Website Plan](WEBSITE_PLAN.md) - Website architecture and content
 
 ---