Reassign nvim-cmp Tab functionality to prioritize GitHub Copilot

## Feature Request: Prioritize GitHub Copilot Tab Completion

### Current Behavior
Currently, our Neovim configuration assigns the Tab key to nvim-cmp functionality:
- Selecting next item in completion menu
- Expanding/navigating snippets via LuaSnip
- Default tab behavior as fallback

Meanwhile, GitHub Copilot's suggestion acceptance is mapped to `` to avoid conflicts.

### Proposed Change
Reassign the nvim-cmp Tab functionality to another key combination and restore Tab as the primary key for accepting GitHub Copilot suggestions.

### Rationale
GitHub Copilot's suggestion acceptance is more valuable in daily coding workflows than nvim-cmp's Tab navigation. The muscle memory of pressing Tab to accept AI suggestions is strong for many developers, and the current setup creates friction.

### Implementation Options

#### Option 1: Swap the Key Mappings
```lua
-- Disable Copilot's tab map initially (keep this line)
vim.g.copilot_no_tab_map = true

-- Map Tab to accept Copilot suggestions
vim.api.nvim_set_keymap('i', '', 'copilot#Accept("")', { expr = true, silent = true })

-- Move nvim-cmp's Tab functionality to Ctrl+J
cmp.setup({
-- other settings...
mapping = cmp.mapping.preset.insert({
-- other mappings...
[''] = cmp.mapping(function(fallback)
if cmp.visible() then
cmp.select_next_item()
elseif luasnip.expand_or_jumpable() then
luasnip.expand_or_jump()
else
fallback()
end
end, { 'i', 's' }),
-- Keep S-Tab as is for previous item
}),
})
```

#### Option 2: Make Tab Context-Aware Between Copilot and nvim-cmp
```lua
-- A more complex but potentially more powerful approach
vim.api.nvim_set_keymap('i', '', 'v:lua.tab_complete()', { expr = true, silent = true })

-- Define the tab_complete function in your init.lua
_G.tab_complete = function()
local copilot_keys = vim.fn['copilot#GetDisplayedSuggestion']()

if copilot_keys.text ~= '' then
return vim.fn['copilot#Accept']("")
elseif require('cmp').visible() then
return require('cmp').mapping.select_next_item()({ behavior = require('cmp').SelectBehavior.Select })
elseif require('luasnip').expand_or_jumpable() then
return require('luasnip').expand_or_jump()
else
return ""
end
end
```

### Files to Update
1. `nvim/lua/plugins/copilot.lua` - Update Copilot key mappings
2. `nvim/init.lua` - Update nvim-cmp configuration in the cmp_setup function
3. `nvim/nvim-cheatsheet.md` - Update documentation to reflect new key mappings
4. `nvim/copilot-cheatsheet.md` - Update with new Tab mapping information

### Benefits
- Aligns with the natural expectation that Tab accepts the visible suggestion
- Improves developer experience with GitHub Copilot
- Reduces cognitive load by using the standard Tab key for its most common modern use case

### Drawbacks
- Requires users to learn a new key combination for nvim-cmp navigation
- May require some adjustment period

### Implementation Priority
High - This would significantly improve the GitHub Copilot experience while requiring minimal changes to the configuration.