feat: Keyboard shortcuts to toggle map overlays

[KidVizious]

What does this PR do?

Adds key bindings to toggle map layers on and off. It also adds both a floating panel and dockable panel with the current list of dynamically created keybinds.

Resolves #635

Type of change

• Bug fix
• New feature
• Performance improvement
• Refactor / code cleanup
• Documentation
• Translation
• Map layer plugin

How to test

1. Press "?" key, panel should appear with a list of keybindings
2. Switch to dockable layout and add a panel, "Keyboard Shortcuts"
3. Panels should respect user's theme choice
4. Press each key listed to toggle the respective layer on/off

Checklist

• App loads without console errors
• Tested in Dark, Light, and Retro themes
• Responsive at different screen sizes (desktop + mobile)
• If touching server.js: caches have TTLs and size caps (we serve 2,000+ concurrent users)
• If adding an API route: includes caching and error handling
• If adding a panel: wired into Modern, Classic, and Dockable layouts
• No hardcoded colors — uses CSS variables (var(--accent-cyan), etc.)
• No .bak, .old, console.log debug lines, or test scripts included

Screenshots (if visual change)

Some sample screenshots are below. I didn't post every combo for brevity sake.

[accius]

Hey, nice work on this — keyboard shortcuts for layer toggling is a great addition and the dual-mode panel (modal + dockable) is well thought out. A few things I'd like addressed before merging:

Bug — Indentation
The closing /> on <KeybindingsPanel> in App.jsx (around line 531) uses a tab instead of spaces. Please fix to match the rest of the codebase.

Bug — Removed translation key
The propagation.heatmap.tooltip.stoplight key was dropped from en.json. Is that intentional? If it's still referenced anywhere that'll break. Can you grep for it and confirm?

Concern — Shortcut stability
The auto-assignment algorithm (first unique letter per layer name) is clever, but it means shortcuts silently reshuffle whenever a layer is added or renamed. A user who learns "G = Greyline" could find G suddenly toggles something else after an update. Would you be open to adding an optional shortcut property to the layer registry so we can pin important ones? The auto-assign can still be the fallback for layers that don't specify one.

Minor — Global coupling
The window.hamclockLayerControls usage works but is a bit fragile. Not a blocker for this PR, but something we should think about cleaning up down the road.

Minor — Static deps on useMemo
layerShortcuts has [] dependencies so it only computes on mount. That's fine if all layers are registered at startup, but worth noting — if we ever load layers dynamically this will need to update.

TL;DR: Fix the indentation and confirm the removed translation key, and this is good to go. The shortcut stability thing can be a follow-up issue. Thanks for putting this together!

[accius]

I am closing this and adding in the fixes as I wouldn't mind having this in tomorrows prod release.

[KidVizious]

@accius I implemented your fixes as well as some other improvements if you want to take another look.

• Layer names now sorted before assigning keys
• Only use layer.id instead of name. Seems like these are used sort of interchangeably between layers but id is usually more sane for keybindings
• Stoplight was in en.json twice
• Fixed tab indentation