feat: fast navigation — gg/G (top/bottom) and Page Up/Down

[shouze]

Context

Part of the 🗂 TUI — Navigation & result management EPIC #66.
Closes #68.

Root cause / motivation

With hundreds of results, line-by-line navigation (↑/↓) is slow. Power users expect Vim-style gg/G jumps and paged scrolling.

What changed

File	Change
src/tui.ts	gg (two consecutive g): jump to first row. G (Shift+G): jump to last row. Page Up / Ctrl+U: scroll up one page. Page Down / Ctrl+D: scroll down one page. Added KEY_PAGE_UP, KEY_PAGE_DOWN, KEY_CTRL_U, KEY_CTRL_D constants. pendingFirstG boolean tracks the first g keypress and is reset on every other key.
src/render.ts	renderHelpOverlay: new gg/G and PgUp/PgDn lines. Status bar hint: gg/G top/bot PgUp/Dn page.
src/render.test.ts	3 new tests: overlay + status bar contain the new shortcut labels.
docs/reference/keyboard-shortcuts.md	New rows in the Navigation table.

How to test manually

bun github-code-search.ts query --org <your-org> <some-query>
# In the TUI:
#   gg → jumps to the very first result
#   G  → jumps to the very last result
#   Page Down / Ctrl+D → scrolls down a full page
#   Page Up  / Ctrl+U → scrolls up  a full page
#   ? → help overlay shows gg/G and PgUp/PgDn entries

Validation

bun test        ✅ 404 pass, 0 fail
bun run lint    ✅ 0 warnings, 0 errors
bun run format:check  ✅
bun run knip    ✅

[Copilot]

Pull request overview

Adds fast navigation shortcuts to the interactive TUI to make moving through large result sets significantly faster, aligning with the TUI navigation epic.

Changes:

• Implement gg (top) and G (bottom) cursor jumps in the TUI.
• Implement Page Up/Down paging via Page Up/Page Down and Vim-style Ctrl+U/Ctrl+D.
• Update help overlay, status bar hints, tests, and keyboard shortcuts documentation to reflect the new bindings.

Reviewed changes

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

File	Description
src/tui.ts	Adds key handling for gg, G, PgUp/PgDn, Ctrl+U/Ctrl+D navigation behaviors.
src/render.ts	Updates help overlay and status bar hint line to document new shortcuts.
src/render.test.ts	Adds tests asserting help overlay and status bar include the new shortcut labels.
docs/reference/keyboard-shortcuts.md	Documents the new navigation shortcuts in the Navigation table.

[shouze]

All 4 review points addressed in commit 54460e9:

1. Multi-character chunk gg — replaced if (key !== "g") pendingFirstG = false with if (!/^g+$/.test(key)) pendingFirstG = false, and changed the g handler condition from key === "g" to /^g+$/.test(key) with pendingFirstG || key.length >= 2. This handles both two separate single-g chunks and a single "gg" chunk from terminals that batch keypresses.

2. G with empty rows (cursor = -1) — added an early continue guard when rows.length === 0 to avoid setting cursor = rows.length - 1 = -1.

3. Page Up at position 0 on a section row — added a follow-up block after the existing while (cursor > 0 && ...) loop:

   if (cursor === 0 && rows[0]?.type === "section") {
     while (cursor < rows.length - 1 && rows[cursor]?.type === "section") cursor++;
   }

   This mirrors the gg behavior (skip section headers at the top).

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

Also rebased onto the updated feat/tui-navigation-result-management (now includes merged PRs #70 and #72). The status bar hint, help overlay, and tests have been updated to reflect all active shortcuts (Z fold-all, gg/G top/bot, PgUp/Dn page, o open). 406 tests, all green.