Merge main into bugfixes-and-improvements - #18

Summary

• merge the latest \ into this branch and resolve the workspace/docs conflicts
• preserve the hidden-session, tab-grouping, per-session shell, and split-resize behavior while keeping the newer workspace module split from \
• refresh the workspace architecture docs to match the merged structure

Verification

• cargo clean
• cargo fmt --all -- --check
• cargo check --workspace --all-targets --all-features
• cargo build --workspace --all-features
• cargo test --all --all-targets --all-features
• cargo clippy --all --all-targets --all-features -- -D warnings
• cargo check -p codirigent-ui --features gpui-full