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/debug/init.lua

@@ -0,0 +1,38 @@
+-- Debug Configuration (DAP)
+local M = {}
+
+function M.setup()
+  local dap = require('dap')
+  local dapui = require('dapui')
+  
+  -- Setup DAP UI with icons and controls
+  dapui.setup({
+    icons = { expanded = '▾', collapsed = '▸', current_frame = '*' },
+    controls = {
+      icons = {
+        pause = '⏸',
+        play = '▶',
+        step_into = '⏎',
+        step_over = '⏭',
+        step_out = '⏮',
+        step_back = 'b',
+        run_last = '▶▶',
+        terminate = '⏹',
+        disconnect = '⏏',
+      },
+    },
+  })
+  
+  -- Automatically open/close DAP UI on debug events
+  dap.listeners.after.event_initialized['dapui_config'] = dapui.open
+  dap.listeners.before.event_terminated['dapui_config'] = dapui.close
+  dap.listeners.before.event_exited['dapui_config'] = dapui.close
+  
+  -- Configure debug adapters for different languages
+  require('plugins.config.debug.adapters').setup()
+  
+  -- Setup debug keymaps
+  require('plugins.config.debug.keymaps').setup()
+end
+
+return M