fix: Replace fmt.Printf with structured logging in authentication flows

[patrickcping]

Description

Fixes MCP protocol compliance violations in authentication wrapper code where fmt.Printf was causing protocol communication issues by writing directly to stdout/stderr. The MCP specification requires structured logging only.

Changes

• internal/auth/client/wrapper.go: Replaced all fmt.Printf calls with structured logging using log.Info with proper key-value pairs
• cmd/session/session.go: Fixed to use correct fmt.Printf for CLI output (CLI commands in cmd/ directory are exempt from MCP logging restrictions)
• Removed format strings (\n), newlines, and trailing punctuation from log messages to follow MCP structured logging patterns

Why This Matters

The MCP specification requires that servers use structured logging only to stderr. Direct output to stdout/stderr via fmt.Printf, fmt.Println, print, or println breaks MCP protocol communication.

This fix ensures the MCP server's authentication flows properly use structured logging as required, preventing interference with protocol communication.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Testing

Test Results

All unit tests passed successfully:

make test

Test Output (All Passed)

=== RUN   TestRootCommand
--- PASS: TestRootCommand (0.00s)
=== RUN   TestLogoutCommand_FromRoot_Basic
--- PASS: TestLogoutCommand_FromRoot_Basic (0.00s)
=== RUN   TestLogoutCommand_Direct_Success
--- PASS: TestLogoutCommand_Direct_Success (0.00s)
=== RUN   TestRunCommand_FromRoot_NoServerRun
--- PASS: TestRunCommand_FromRoot_NoServerRun (0.00s)
=== RUN   TestSessionCommand_FromRoot_Basic
--- PASS: TestSessionCommand_FromRoot_Basic (0.00s)
PASS
ok      github.com/pingidentity/pingone-mcp-server/cmd  (cached)
...
All tests passed

Manual Validation

• ✅ Authentication flows use structured logging
• ✅ No fmt.Printf in MCP server code (internal/ packages)
• ✅ CLI commands still output to users correctly
• ✅ MCP protocol communication not interfered with

Checklist

• Code follows MCP specification (especially logging requirements)
• make test passes
• Error handling follows project patterns
• All code uses structured logging (no fmt.Printf in internal/)
• Tests cover functionality
• PR template is filled out completely

Related Issues

Fixes authentication flow logging issues that caused warnings in MCP clients due to protocol violations.

Additional Context

This is part 1 of a 2-part change. Part 2 (separate PR) will add automated enforcement mechanisms (golangci-lint configuration, Makefile checks, and documentation) to prevent future violations.