refactor: Complete modular migration from kickstart.nvim

Major architectural overhaul to transform the flat kickstart.nvim structure
  into a maintainable, modular configuration while preserving upstream sync capability.

  ## Structure Changes
  - Migrated from flat `lua/custom/` to organized `lua/core/` and `lua/plugins/`
  - Separated plugin specs from configs: `lua/plugins/spec/` and `lua/plugins/config/`
  - Complex configs (LSP, Debug) now use directory structure with sub-modules:
    - `lsp/init.lua`, `lsp/servers.lua`, `lsp/keymaps.lua`
    - `debug/init.lua`, `debug/adapters.lua`, `debug/keymaps.lua`

  ## Core Improvements
  - Created dedicated core modules: options, keymaps, autocmds, bootstrap, health
  - Added comprehensive health check (`lua/core/health.lua`) for diagnostics
  - Simplified init.lua to just orchestrate module loading
  - Better separation of concerns throughout

  ## Plugin Updates
  - Fixed Blink.cmp configuration (removed invalid fuzzy options)
  - Integrated Copilot with Blink.cmp for unified completion experience
  - Added autopairs and indent-line from kickstart examples
  - Optimized for Nix development environments (removed venv assumptions)

  ## Documentation
  - Updated README with modular structure and kickstart sync instructions
  - Created comprehensive KEYBIND_ANALYSIS.md with all mappings
  - Added modular.txt help documentation
  - Created TODO_TEST.md checklist for testing

  ## Benefits
  - Easier to maintain and extend
  - Clean separation allows upstream kickstart merges without conflicts
  - Scalable architecture for adding new languages/tools
  - Better code organization and discoverability

  All kickstart functionality preserved while gaining modularity and maintainability.

lua/plugins/config/blink.lua

@@ -0,0 +1,126 @@
+-- Blink.cmp Configuration
+local M = {}
+
+function M.setup()
+  require('blink.cmp').setup({
+    -- Keymap configuration
+    keymap = {
+      preset = 'default',
+      ['<C-space>'] = { 'show', 'show_documentation', 'hide_documentation' },
+      ['<C-e>'] = { 'hide' },
+      ['<C-y>'] = { 'select_and_accept' },
+      
+      ['<C-p>'] = { 'select_prev', 'fallback' },
+      ['<C-n>'] = { 'select_next', 'fallback' },
+      
+      ['<C-b>'] = { 'scroll_documentation_up', 'fallback' },
+      ['<C-f>'] = { 'scroll_documentation_down', 'fallback' },
+      
+      ['<Tab>'] = { 'snippet_forward', 'fallback' },
+      ['<S-Tab>'] = { 'snippet_backward', 'fallback' },
+    },
+    
+    -- Appearance configuration
+    appearance = {
+      use_nvim_cmp_as_default = true,
+      nerd_font_variant = 'mono',
+    },
+    
+    -- Sources configuration with Copilot integration
+    sources = {
+      default = { 'lsp', 'path', 'snippets', 'buffer', 'copilot' },
+      providers = {
+        copilot = {
+          name = 'copilot',
+          module = 'blink-cmp-copilot',
+          score_offset = 100,
+          async = true,
+          transform_items = function(_, items)
+            -- Add copilot icon to copilot suggestions
+            for _, item in ipairs(items) do
+              item.kind = 'Copilot'
+            end
+            return items
+          end,
+        },
+      },
+    },
+    
+    -- Command line configuration (new API)
+    cmdline = {
+      enabled = false, -- Disable cmdline completion for now
+    },
+    
+    -- Signature help configuration
+    signature = {
+      enabled = true,
+      window = {
+        border = 'rounded',
+      },
+    },
+    
+    -- Completion configuration
+    completion = {
+      accept = {
+        -- Auto-insert brackets for functions
+        auto_brackets = {
+          enabled = true,
+        },
+      },
+      menu = {
+        draw = {
+          columns = {
+            { 'label', 'label_description', gap = 1 },
+            { 'kind_icon', 'kind' }
+          },
+        },
+        border = 'rounded',
+        winblend = 0,
+      },
+      documentation = {
+        auto_show = true,
+        auto_show_delay_ms = 200,
+        window = {
+          border = 'rounded',
+        },
+      },
+      ghost_text = {
+        enabled = true,
+      },
+    },
+    
+    -- Fuzzy matching configuration
+    fuzzy = {
+      -- Use Rust implementation for better performance
+      implementation = 'prefer_rust_with_warning',
+      -- Allow typos based on keyword length
+      max_typos = function(keyword)
+        return math.floor(#keyword / 4)
+      end,
+      -- Track frequently/recently used items
+      use_frecency = true,
+      -- Boost items matching nearby words
+      use_proximity = true,
+      -- Prebuilt binaries configuration
+      prebuilt_binaries = {
+        download = true,
+      },
+    },
+    
+    -- Snippet configuration
+    snippets = {
+      expand = function(snippet)
+        -- Use native snippet expansion if available
+        if vim.snippet then
+          vim.snippet.expand(snippet)
+        else
+          -- Fallback to basic expansion
+          local insert = string.gsub(snippet, '%$%d+', '')
+          vim.api.nvim_put({ insert }, 'c', true, true)
+        end
+      end,
+    },
+  })
+end
+
+return M