fix(tui): handle CR in MCP SSE fields

[cyq1017]

Fixes #1309

Summary

• trim trailing \r from MCP SSE event: and data: field values before dispatching endpoint/message events
• keep existing LF and CRLF event separator handling unchanged
• add regression coverage for CR-safe field parsing and a mixed CRLF-line/LF-separator endpoint discovery case

Verification

• cargo fmt --all -- --check
• cargo test -p codewhale-tui sse_
• git diff --check

[gemini-code-assist]

Code Review

This pull request improves the handling of carriage returns in Server-Sent Events (SSE) by updating the sse_field_value helper to strip trailing \r characters and adding comprehensive tests for mixed line endings. A review comment correctly identifies a redundant trim operation in the event processing loop that can be removed to simplify the code.

[gemini-code-assist]

The explicit trimming of \r here is redundant because the sse_field_value helper has been updated to handle trailing carriage returns internally (see line 1092). Removing this line simplifies the loop and avoids unnecessary double-trimming of the string slice.

                    if let Some(value) = sse_field_value(line, "event:") {