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- Clean up outdated roadmap items and fix inconsistencies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/OVERVIEW.md

@@ -150,6 +150,15 @@ Time.sleep(1000)  // milliseconds
 let obj = Json.parse("{\"name\": \"Alice\"}")
 let str = Json.stringify(obj)
 
+// SQL database effects
+let db = Sql.openMemory()
+Sql.execute(db, "CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)")
+Sql.execute(db, "INSERT INTO users (name) VALUES ('Alice')")
+let users = Sql.query(db, "SELECT * FROM users")
+Sql.beginTx(db)
+Sql.commit(db)  // or Sql.rollback(db)
+Sql.close(db)
+
 // Module system
 import mymodule
 import utils/helpers as h
@@ -179,10 +188,6 @@ fn processModern(x: Int @v2+): Int = x  // v2 or later
 fn processAny(x: Int @latest): Int = x  // any version
 ```
 
-### Planned (Not Yet Fully Implemented)
-
-- **Auto-migration Generation**: Migration bodies stored, execution pending
-
 ---
 
 ## Primary Use Cases
@@ -235,7 +240,7 @@ Quick iteration with type inference and a REPL.
 |------------|-------------|
 | **New Paradigm** | Effects require learning new concepts |
 | **Small Ecosystem** | Community packages just starting |
-| **No Package Registry** | Can share code via git/path, no central registry yet |
+| **Young Package Registry** | Package registry available, but small ecosystem |
 | **Early Stage** | Bugs likely, features incomplete |
 
 ---
@@ -374,18 +379,10 @@ Values + Effects        C Code → GCC/Clang
 - ✅ Formatter
 
 **In Progress:**
-1. **Schema Evolution** - Type-declared migrations working, auto-generation pending
-2. **Error Message Quality** - Context lines shown, suggestions partial
-3. **Memory Management** - RC working for lists/boxed, closures/ADTs pending
-
-**Recently Completed:**
-- ✅ **JavaScript Backend** - Full language support, browser & Node.js
-- ✅ **Dom Effect** - 40+ browser manipulation operations
-- ✅ **Html Module** - Type-safe HTML construction (Elm-style)
-- ✅ **TEA Runtime** - The Elm Architecture for web apps
-- ✅ **Package Manager** - `lux pkg` with git/path dependencies, module integration
+1. **Memory Management** - RC working for lists/boxed, closures/ADTs pending
+2. **Serialization Codecs** - JSON codec generation for versioned types
 
 **Planned:**
-4. **SQL Effect** - Database access (as a package)
-5. **Package Registry** - Central repository for sharing packages
-6. **Behavioral Type Verification** - Total, idempotent, deterministic checking
+- **Connection Pooling** - Pool database connections
+- **WASM Backend** - WebAssembly compilation target
+- **Stream Processing** - Stream effect for data pipelines