Consolidate nvim-cmp setup to eliminate multiple configuration calls

[Copilot]

Addresses review feedback to fix multiple cmp.setup() invocations and duplicate cmdline configurations in nvim-cmp.lua, which made the config difficult to reason about due to potential setting overrides.

Changes:

• Merged 3 separate cmp.setup() calls into single consolidated configuration containing all features (snippet, window, mapping, sources, formatting)
• Removed duplicate cmdline completion configurations for /, ?, and :
• Cleaned up commented example code and redundant documentation

Before (163 lines):

cmp.setup({ snippet = {...}, mapping = {...}, sources = {...} })
cmp.setup.cmdline({ '/', '?' }, {...})
cmp.setup.cmdline(':', {...})
cmp.setup({ snippet = {...}, window = {...}, mapping = {...}, sources = {...} })  -- duplicate
cmp.setup.cmdline({ '/', '?' }, {...})  -- duplicate
cmp.setup.cmdline(':', {...})  -- duplicate
cmp.setup({ formatting = {...} })  -- third setup call

After (82 lines):

cmp.setup({
  snippet = {...},
  window = {...},
  mapping = {...},
  sources = {...},
  formatting = {...}  -- all in one place
})
cmp.setup.cmdline({ '/', '?' }, {...})  -- defined once
cmp.setup.cmdline(':', {...})  -- defined once

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