fix: Remove REPLACE keyword to avoid conflict with REPLACE() function

The REPLACE token was conflicting with the existing REPLACE() string
function, breaking the showcase_deterministic formal test.

**Problem:**
- Added Token::Replace as a keyword for SELECT * REPLACE
- This broke `REPLACE('text', 'old', 'new')` function calls
- Parser error: "Unexpected token in primary expression: Replace"

**Solution:**
- Keep only EXCLUDE as a keyword token
- REPLACE will be handled contextually in the parser
- When we implement SELECT * REPLACE, we'll check for REPLACE
  as an identifier in the right context, not as a keyword

**Test Results:**
- ✅ REPLACE() function works again
- ✅ showcase_deterministic formal test passes
- ✅ All 119 example tests passing

**Lesson Learned:**
When adding new keywords, always check if they conflict with
existing function names. Use contextual parsing when needed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: TimelordUK

src/sql/parser/lexer.rs

@@ -55,7 +55,8 @@ pub enum Token {
     Partition, // PARTITION keyword for window functions
     By,        // BY keyword (used with PARTITION BY, ORDER BY)
     Exclude,   // EXCLUDE keyword (for SELECT * EXCLUDE)
-    Replace,   // REPLACE keyword (for SELECT * REPLACE)
+    // Note: REPLACE is NOT a keyword - it's handled as a function name
+    // to avoid conflicting with the REPLACE() string function
 
     // Window frame keywords
     Rows,      // ROWS frame type
@@ -154,7 +155,6 @@ impl Token {
             "INTO" => Some(Token::Into),
             "DISTINCT" => Some(Token::Distinct),
             "EXCLUDE" => Some(Token::Exclude),
-            "REPLACE" => Some(Token::Replace),
             "CASE" => Some(Token::Case),
             "WHEN" => Some(Token::When),
             "THEN" => Some(Token::Then),
@@ -244,7 +244,6 @@ impl Token {
             Token::Into => Some("INTO"),
             Token::Distinct => Some("DISTINCT"),
             Token::Exclude => Some("EXCLUDE"),
-            Token::Replace => Some("REPLACE"),
             Token::Case => Some("CASE"),
             Token::When => Some("WHEN"),
             Token::Then => Some("THEN"),
@@ -863,7 +862,6 @@ impl Lexer {
                     "END" => Token::End,
                     "DISTINCT" => Token::Distinct,
                     "EXCLUDE" => Token::Exclude,
-                    "REPLACE" => Token::Replace,
                     "OVER" => Token::Over,
                     "PARTITION" => Token::Partition,
                     "BY" => Token::By,

src/text_navigation.rs

@@ -189,7 +189,6 @@ impl TextNavigator {
             Token::End => "END",
             Token::Distinct => "DISTINCT",
             Token::Exclude => "EXCLUDE",
-            Token::Replace => "REPLACE",
             Token::Over => "OVER",
             Token::Partition => "PARTITION",
             Token::By => "BY",