Keyboard shortcuts modal is out of sync with actual keybindings

[NisargJasani0602]

Follow-up to #4222 (see this comment for context) — KeyboardShortcutModal.jsx has drifted from what's actually wired up in keymaps.js. A few known discrepancies:

Advertised but not implemented:

• The modal lists {Ctrl/Cmd}+H for "Replace," but there's no replace command wired up anywhere in keymaps.js. Worth deciding: implement it (CodeMirror 6's search panel already supports replace, just needs to be exposed on this shortcut), or remove the claim from the modal if it's not planned.

Implemented but not advertised:

• Ctrl-Shift-Up/Down (Cmd-Ctrl-Up/Down on Mac) — move line up/down, added in Fix Ctrl+Shift+Up/Down no longer moving lines #4250.
• Shift-Ctrl-D (Shift-Cmd-D on Mac) — duplicate line, and Ctrl-Up/Down (Ctrl-Alt-Up/Down on Mac) — scroll without moving cursor, both pending in a follow-up PR.

Proposal

1. Decide the fate of the Replace shortcut (implement vs. remove from modal).
2. Add entries to KeyboardShortcutModal.jsx for the shortcuts above.

Happy to take this on.

[welcome]

Welcome! 👋 Thanks for opening your first issue here! And to ensure the community is able to respond to your issue, be sure to follow the issue template if you haven't already.

[NisargJasani0602]

Found a few more discrepancies while continuing the audit:

Phantom, needs a decision:

• {Ctrl/Cmd}+. "Comment Line" — nothing implements this. Only Mod-/ actually toggles comments. Worth restoring though: I found the old pre-CM6 config explicitly bound this as a fallback (// Note: most adblockers use the shortcut ctrl+.), so it looks like a deliberate accessibility/compatibility choice that got lost in the migration, not just a stale doc entry.
• F2/Ctrl+F2 "Rename Variable" — also nothing implements this. There's dead code for it (rename-variable.js, showRenameDialog.jsx), but nothing in the entire client codebase imports or uses them — no keydown listener exists anywhere. Unlike Mod-., I haven't verified this dead code even works, so before deciding to wire it up I'd want to check that first.

For both of these: implement (restore/wire up) or drop the claim from the modal? Same open question as the Replace shortcut on #4255.

Mislabeled — the modal's "Reference" entry claims Shift+Right, but the actual binding in keymaps.js is plain ArrowRight (no Shift). Trivial fix, just a label correction.

Bonus, undocumented but real — found these while checking global shortcuts: Ctrl+B/Cmd+B (toggle sidebar) and Ctrl+`/Cmd+` (toggle console).

Proposed direction, to keep things reviewable:

1. Fix the Shift+Right label — trivial, can do immediately.
2. Document Ctrl+B/Cmd+B and Ctrl+`/Cmd+` — trivial, same PR as *1.
3. Mod-. and F2 — need your input on implement-vs-drop before I write any code.

Let me know your read on #3, or if you'd rather I just pick a default for each.