optimize TUI load times

[skarim]

Optimize view/modify TUI load time with parallel fetching

• Deduplicate API calls: syncStackPRs now returns PRDetails for LoadBranchNodes to reuse, eliminating redundant FindPRDetailsForBranch calls
• Parallelize API calls in syncStackPRs (capped at 6 concurrent requests)
• Parallelize git operations in LoadBranchNodes (capped at 4 concurrent)
• Show "Loading stack..." indicator for interactive sessions

---

_{Stack created with GitHub Stacks CLI • Give Feedback 💬}

[Copilot]

Pull request overview

This PR aims to reduce view / modify TUI startup latency by avoiding redundant GitHub API calls and doing branch data loading in parallel, while also adding a lightweight “Loading stack…” indicator in interactive sessions.

Changes:

• syncStackPRs now returns per-branch PRDetails and performs API requests concurrently (capped).
• LoadBranchNodes accepts optional pre-fetched PR details and parallelizes git-derived branch computations (capped).
• view / modify show and clear a “Loading stack…” indicator during the sync phase.

Show a summary per file

File	Description
internal/tui/stackview/data.go	Parallelizes per-branch git computations and reuses pre-fetched PR details to avoid extra API calls.
internal/tui/stackview/data_test.go	Updates tests for the new LoadBranchNodes function signature.
cmd/view.go	Adds interactive loading indicator and threads returned PR details into the TUI path.
cmd/utils.go	Makes syncStackPRs return PR details and parallelizes PR discovery/sync with concurrency limits.
cmd/modify.go	Shows loading indicator during PR sync and reuses returned PR details for TUI node loading.

Copilot's findings

Tip

Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

• Files reviewed: 5/5 changed files
• Comments generated: 1