fix(ai): bind Shift+Cmd+I to Focus Chat (was only Ctrl+Cmd+I)

[ndemianc]

The bug

Shift+Cmd+I does nothing — the LevelCode AI chat only opens from the Command Palette ("AI: Focus Chat") or Ctrl+Cmd+I.

Why

The command was fine; only its keybinding was wrong. The single contributed binding was ctrl+cmd+i, and Shift+Cmd+I is already claimed in the Code-OSS base by the built-in VS Code chat's "Open Chat (Agent)" action:

// vscode/src/vs/workbench/contrib/chat/browser/actions/chatActions.ts:593
primary: KeyMod.CtrlCmd | KeyMod.Shift | KeyCode.KeyI,   // = Shift+Cmd+I on macOS
when: ContextKeyExpr.has(`config.${ChatConfiguration.AgentEnabled}`)

LevelCode ships its own chat and doesn't enable the built-in one, so Shift+Cmd+I fired a dead/stripped action instead of LevelCode's chat.

Fix

An explicit shift+cmd+i → levelcode.ai.focus binding. This reliably wins over the base action because bundled-extension keybindings register at a higher weight than workbench defaults — verified in source, not assumed:

// keybindingService.ts:633-635
weight = KeybindingWeight.BuiltinExtension /*300*/ + idx;   // bundled ext
weight = KeybindingWeight.ExternalExtension /*400*/ + idx;  // external ext
// base chat action is WorkbenchContrib = 200 → the extension binding wins

Platform	New chat shortcut
macOS	Shift+Cmd+I (what was requested) — mirrors VS Code's own chat
Windows	Ctrl+Shift+I
Linux	Ctrl+Alt+Shift+I (dodges Dev Tools, same as VS Code's chat does)

The existing Ctrl+Cmd+I is kept as a second binding, so no one loses their current shortcut. This also closes a latent gap: the old "key": "ctrl+cmd+i" used cmd, which is invalid on Windows/Linux — those platforms had no chat shortcut at all.

Verification

• package.json is valid; the bindings resolve to shift+cmd+i on macOS (+ the cross-platform set).
• The weight-override mechanism is confirmed in the Code-OSS source.
• Needs a build smoke-test for the actual keypress — there's no editor host in this environment to press the key. The mechanism is verified; the end-to-end press is not.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes LevelCode AI chat focus keybinding so Shift+Cmd+I works on macOS (and adds sensible defaults for Windows/Linux), preventing the shortcut from triggering the stripped/built-in chat action.

Changes:

• Add shift+cmd+i (macOS) / ctrl+shift+i (Windows default) / ctrl+alt+shift+i (Linux) keybinding for levelcode.ai.focus.
• Keep the existing ctrl+cmd+i binding for levelcode.ai.focus as an additional shortcut.

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