#30528 base red: cmux-tui clippy collapsible_if in Cloud repos (#30361)

The cmux-tui `clippy (changed cmux-tui packages)` job fails on feat-cmux-next since #30361 for every PR that touches cmux-tui:

• `crates/acpmux/src/agent_tools.rs:590` collapsible_if
• `crates/acpmux/src/cloud_repo_mcp.rs:155` collapsible_if
• `crates/cmux-tui-core/src/cloud_repos/engine.rs:241,242` collapsible_if
• `crates/cmux-tui-core/src/cloud_repos/runtime.rs:150` collapsible_if
• `crates/cmux-tui-core/src/cloud_repos/runtime.rs:279` semicolon_if_nothing_returned

Seen on #28215 (clippy run 41284420987), which touches none of these files. The fix turns the nested ifs into let-chains and adds the semicolon. No behavior change.

Small (lint-only, 4 files).

Agent session: agent session

🤖 Generated with Claude Code

---

Summary by cubic

Fixes the cmux-tui clippy job being red on feat-cmux-next by resolving five collapsible_if lints and one missing-semicolon lint in the Cloud repository code.

• Converts nested if let blocks into let-chains in cloud repo discovery, add, and retry flows.
• Adds the missing semicolon after sleep in cloud_repos/runtime.rs.
• No behavior change; affects only lint-passing code in acpmux and cmux-tui-core.