Keep composer controls compact

[oshtz]

Summary

• keep the composer toolbar left-aligned and compact
• size the project picker to its label while preserving responsive truncation
• remove the redundant slash toolbar button while retaining typed commands and shortcut access
• release v0.2.29 with summary-only notes and no update cards

Verification

• git diff --check
• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace
• cargo clippy --manifest-path apps/desktop/src-tauri/Cargo.toml --all-targets -- -D warnings
• cargo test --manifest-path apps/desktop/src-tauri/Cargo.toml --lib with the Windows test manifest linker flags
• pnpm -C apps/desktop verify:release-notes
• pnpm -C apps/desktop verify