perf: replace tokio full features with explicit list

## Context

Root binary uses `tokio = { features = ["full"] }` compiling all features. Expected 10-15% tokio compile time reduction with explicit list.

## Proposed change

```toml
tokio = { workspace = true, features = ["macros", "rt-multi-thread", "sync", "signal", "time"] }
```

## Affected crates

Root binary

## Ref

`.local/plan/performance-audit.md` — Issue 1.2