feat: global fold/unfold — Z to collapse or expand all repositories at once

[shouze]

Context

Part of the 🗂 TUI — Navigation & result management EPIC #66.
Closes #67.

Root cause / motivation

The TUI only allows folding/unfolding one repo at a time (← / →). With many repositories in the result set, collapsing everything to get a quick overview required pressing ← dozens of times.

What changed

File	Change
src/tui.ts	Z keypress: fold all repos if any is unfolded; unfold all if all are folded. Clamps cursor + scrollOffset after bulk fold.
src/render.ts	renderHelpOverlay: new line Z fold / unfold all repos. Status bar hint: Z fold-all.
src/render.test.ts	2 new tests: overlay contains Z + fold / unfold all repos; status bar contains Z fold-all.
docs/reference/keyboard-shortcuts.md	New row in the Navigation table.

How to test manually

bun github-code-search.ts query --org <your-org> <some-query>
# In the TUI: press Z → all repos collapse
# Press Z again → all repos expand
# Press ? → help overlay shows the Z entry

Validation

bun test        ✅ 403 pass, 0 fail
bun run lint    ✅ 0 warnings, 0 errors
bun run format:check  ✅
bun run knip    ✅

[Copilot]

Pull request overview

Adds a global fold/unfold shortcut to the interactive TUI so users can collapse/expand all repositories at once, improving navigation when many repos are present.

Changes:

• Add Z key handling in the TUI to fold all repos if any are unfolded, otherwise unfold all.
• Update TUI help overlay + status bar hints to document the new shortcut.
• Add tests and update the keyboard shortcuts reference docs.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/tui.ts	Implements Z global fold/unfold behavior and cursor/scroll clamping after bulk fold.
src/render.ts	Documents Z in the help overlay and status bar hint line.
src/render.test.ts	Adds regression tests asserting Z appears in help overlay and status bar hints.
docs/reference/keyboard-shortcuts.md	Documents Z in the Navigation shortcuts table.

[shouze]

Addressed in commit 9cf3ba2:

Cursor preservation (lines 398-401): implemented the exact approach suggested — when Z folds all repos from a repo or extract row, the cursor is now mapped to that row's repo header in newRows (via findIndex r.type === "repo" && r.repoIndex === row.repoIndex), with a fallback to numeric clamp if the header is somehow not found.

Intro sentence in keyboard-shortcuts.md: updated to "Keys are case-sensitive — most use lowercase letters, but a few bindings (such as Z and G) require an uppercase letter."

Closes #67 reference: confirmed correct — #67 is the "global fold/unfold" issue, which is precisely what this PR implements.