fix(sequential-thinking): convert to modern TypeScript SDK APIs (#3014)

* fix(sequential-thinking): convert to modern TypeScript SDK APIs

Convert the sequential-thinking server to use the modern McpServer API
instead of the low-level Server API.

Key changes:
- Replace Server with McpServer from @modelcontextprotocol/sdk/server/mcp.js
- Use registerTool() method instead of manual request handlers
- Use Zod schemas directly in inputSchema/outputSchema
- Add structuredContent to tool responses
- Fix type literals to use 'as const' assertions

The modern API provides:
- Less boilerplate code
- Better type safety with Zod
- More declarative tool registration
- Cleaner, more maintainable code

* fix: exclude test files from TypeScript build

Add exclude for test files and vitest.config.ts to tsconfig

* refactor: remove redundant validation now handled by Zod

Zod schema already validates all required fields and types. Removed
validateThoughtData() method and kept only business logic validation
(adjusting totalThoughts if needed).

* fix(sequentialthinking): add Zod validation to processThought method

The modern API migration removed manual validation from processThought(),
but tests call this method directly, bypassing the Zod validation in the
tool registration layer. This commit adds Zod validation directly in the
processThought() method to ensure validation works both when called via
MCP and when called directly (e.g., in tests).

Also improves error message formatting to match the expected error
messages in the tests.

* refactor: simplify by removing redundant validation

Since processThought() is only called through the tool registration in
production, validation always happens via Zod schemas at that layer.
Removed redundant validation logic from processThought() and updated
tests to reflect this architectural decision.

Changes:
- Remove Zod validation from processThought() method
- Accept ThoughtData type instead of unknown
- Remove 10 validation tests that are now handled at tool registration
- Add comment explaining validation approach

src/sequentialthinking/__tests__/lib.test.ts

@@ -22,107 +22,8 @@ describe('SequentialThinkingServer', () => {
     server = new SequentialThinkingServer();
   });
 
-  describe('processThought - validation', () => {
-    it('should reject input with missing thought', () => {
-      const input = {
-        thoughtNumber: 1,
-        totalThoughts: 3,
-        nextThoughtNeeded: true
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid thought');
-    });
-
-    it('should reject input with non-string thought', () => {
-      const input = {
-        thought: 123,
-        thoughtNumber: 1,
-        totalThoughts: 3,
-        nextThoughtNeeded: true
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid thought');
-    });
-
-    it('should reject input with missing thoughtNumber', () => {
-      const input = {
-        thought: 'Test thought',
-        totalThoughts: 3,
-        nextThoughtNeeded: true
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid thoughtNumber');
-    });
-
-    it('should reject input with non-number thoughtNumber', () => {
-      const input = {
-        thought: 'Test thought',
-        thoughtNumber: '1',
-        totalThoughts: 3,
-        nextThoughtNeeded: true
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid thoughtNumber');
-    });
-
-    it('should reject input with missing totalThoughts', () => {
-      const input = {
-        thought: 'Test thought',
-        thoughtNumber: 1,
-        nextThoughtNeeded: true
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid totalThoughts');
-    });
-
-    it('should reject input with non-number totalThoughts', () => {
-      const input = {
-        thought: 'Test thought',
-        thoughtNumber: 1,
-        totalThoughts: '3',
-        nextThoughtNeeded: true
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid totalThoughts');
-    });
-
-    it('should reject input with missing nextThoughtNeeded', () => {
-      const input = {
-        thought: 'Test thought',
-        thoughtNumber: 1,
-        totalThoughts: 3
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid nextThoughtNeeded');
-    });
-
-    it('should reject input with non-boolean nextThoughtNeeded', () => {
-      const input = {
-        thought: 'Test thought',
-        thoughtNumber: 1,
-        totalThoughts: 3,
-        nextThoughtNeeded: 'true'
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid nextThoughtNeeded');
-    });
-  });
+  // Note: Input validation tests removed - validation now happens at the tool
+  // registration layer via Zod schemas before processThought is called
 
   describe('processThought - valid inputs', () => {
     it('should accept valid basic thought', () => {
@@ -275,19 +176,6 @@ describe('SequentialThinkingServer', () => {
   });
 
   describe('processThought - edge cases', () => {
-    it('should reject empty thought string', () => {
-      const input = {
-        thought: '',
-        thoughtNumber: 1,
-        totalThoughts: 1,
-        nextThoughtNeeded: false
-      };
-
-      const result = server.processThought(input);
-      expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Invalid thought');
-    });
-
     it('should handle very long thought strings', () => {
       const input = {
         thought: 'a'.repeat(10000),
@@ -349,25 +237,6 @@ describe('SequentialThinkingServer', () => {
       expect(result.content[0]).toHaveProperty('text');
     });
 
-    it('should return correct error structure on failure', () => {
-      const input = {
-        thought: 'Test',
-        thoughtNumber: 1,
-        totalThoughts: 1
-        // missing nextThoughtNeeded
-      };
-
-      const result = server.processThought(input);
-
-      expect(result).toHaveProperty('isError', true);
-      expect(result).toHaveProperty('content');
-      expect(Array.isArray(result.content)).toBe(true);
-
-      const errorData = JSON.parse(result.content[0].text);
-      expect(errorData).toHaveProperty('error');
-      expect(errorData).toHaveProperty('status', 'failed');
-    });
-
     it('should return valid JSON in response', () => {
       const input = {
         thought: 'Test thought',