docs(readme): add keyboard shortcuts guide

[hugows]

Had a hard time finding out keyboard shortcuts, for some reason.

[greptile-apps]

Greptile Summary

This PR adds a curated Keyboard shortcuts section to the README, giving GitHub visitors a quick reference for navigation, view, and review controls without opening the app. All listed shortcuts were verified against the source implementation (keyboard.ts, useAppKeyboardShortcuts.ts) and are accurate.

• README.md: Adds Navigation, View, and Review subsections with 18 shortcuts; j/k, PageDown/PageUp, and Esc are correctly included as aliases even though they don't appear in the in-app HelpDialog.
• CHANGELOG.md: Adds a single [Unreleased] entry describing the new section.

Confidence Score: 4/5

Safe to merge — all shortcuts listed are verified accurate against the source; the only gap is the omitted Shift modifier hint for faster horizontal scrolling.

Every shortcut in the new section was cross-checked against keyboard.ts and useAppKeyboardShortcuts.ts and all are correct. The Shift+←/→ faster horizontal scroll is implemented and shown in the in-app HelpDialog but not mentioned in the README, leaving readers with an incomplete picture of the horizontal scroll controls.

README.md — specifically the horizontal scroll entry on line 62, where the Shift modifier hint is missing.

Important Files Changed

Filename	Overview
README.md	Adds a Keyboard shortcuts section with Navigation, View, and Review subsections. All listed shortcuts verified correct against the source implementation; the Shift+←/→ faster horizontal scroll modifier present in both the source and in-app HelpDialog is omitted.
CHANGELOG.md	Adds a one-line entry under [Unreleased] → Added describing the new README keyboard shortcuts section. Accurate and appropriately placed.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Key pressed] --> B{Active mode}
    B -->|menu open| C[handleMenuShortcut\nEsc close, arrows navigate]
    B -->|pager mode| D[handlePagerShortcut\nq or Esc quit, scroll keys]
    B -->|help shown| E[handleHelpShortcut\nEsc closes help]
    B -->|filter focus| F[handleFilterShortcut\nTab toggles focus]
    B -->|normal| G[handleAppShortcut]
    G --> H[Navigation shortcuts\nup/down j/k, space/f/pagedown\nb/pageup/shiftspace, d/u\nhome/end, brackets, arrows]
    G --> I[View shortcuts\n1/2/0 layouts, s t a, l/w/m]
    G --> J[Review shortcuts\nslash, tab, F10, r, q/esc, ?]

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
README.md:62
The in-app `HelpDialog` describes horizontal scrolling as `← / →` with "(Shift = faster)", meaning `Shift+←` / `Shift+→` jumps 8 columns at a time (`FAST_CODE_HORIZONTAL_SCROLL_COLUMNS = 8`) versus 1 column without Shift. Omitting this from the README leaves users unaware of a handy shortcut that's documented in the app itself.

```suggestion
- `←` / `→` — scroll code horizontally (`Shift+←` / `Shift+→` for faster scrolling)
```

_{Reviews (1): Last reviewed commit: "docs(readme): add keyboard shortcuts gui..." | Re-trigger Greptile}

[benvinegar]

I agree with mentioning the shortcuts, but I don't think this is how I would place them in the readme. I'm particular over how the README looks. I'll probably take this and tune it.