fix(cli): redirect stderr before MCP loading to prevent terminal pollution

[n-WN]

Related Issue

Resolves #1214 — Verbose MCP debug messages printed to console when starting with -C flag and OAuth MCP servers.

Also related: #1215 (attempted fix, still open), #1501 (closed without merge).

Description

MCP server subprocesses (e.g. mcp-remote) write debug and OAuth logs to stderr. Previously, redirect_stderr_to_logger() was called after KimiCLI.create(), which meant MCP server stderr output during startup went directly to the user's terminal, polluting the TUI.

Root Cause

enable_logging(debug, redirect_stderr=False)   ← line 343: stderr NOT redirected yet
    ...
instance = await KimiCLI.create(...)           ← line 530: MCP servers start here
    ...                                           stderr noise goes to terminal ❌
redirect_stderr_to_logger()                    ← line 549: too late

Fix

Move redirect_stderr_to_logger() to just before KimiCLI.create(). At this point CLI argument parsing has already completed, so Typer/Click startup errors are no longer a concern. Fatal errors from create() remain visible because _emit_fatal_error() writes to the saved original stderr fd (not affected by the redirect).

enable_logging(debug, redirect_stderr=False)   ← line 343: still deferred here
    ...
redirect_stderr_to_logger()                    ← line 535: NOW redirected ✅
instance = await KimiCLI.create(...)           ← line 537: MCP stderr → log file

Before / After

Tested with a noisy MCP server that writes 5 debug lines to stderr during startup:

# Before (upstream/main):
$ kimi --mcp-config-file noisy.json --yolo -p 'say hi' 2>&1 | cat
[mcp-remote DEBUG] Connecting to OAuth provider... attempt 1
[mcp-remote DEBUG] Connecting to OAuth provider... attempt 2
[mcp-remote DEBUG] Connecting to OAuth provider... attempt 3
[mcp-remote DEBUG] Connecting to OAuth provider... attempt 4
[mcp-remote DEBUG] Connecting to OAuth provider... attempt 5
• Hello! 👋 How can I help you today?

# After (this branch):
$ kimi --mcp-config-file noisy.json --yolo -p 'say hi' 2>&1 | cat
• Hello! 👋 I'm Kimi Code CLI, your software engineering assistant. How can I help you today?

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue, if any.
• I have run make gen-changelog to update the changelog.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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