Restructure modules/shared and update all imports

- Delete 2024-12-rework/ folder
- Rename modules/hosts/common to modules/shared, then split into:
  - modules/shared/home/general
  - modules/shared/home/linux
  - modules/shared/nixos
- Update all import paths throughout the codebase
- Update lib/*.nix to use new paths
- Fix hardcoded /Users/${username} to use config.home.homeDirectory
- Update README and examples/flake-structure.nix

modules/shared/files/nvim/lua/plugins/completions.lua

@@ -0,0 +1,49 @@
+return {
+  {
+    "hrsh7th/nvim-cmp",
+    config = function()
+      local cmp = require("cmp")
+      require("luasnip.loaders.from_vscode").lazy_load()
+
+      cmp.setup({
+        snippet = {
+          expand = function(args)
+            require("luasnip").lsp_expand(args.body)
+          end,
+        },
+        window = {
+          completion = cmp.config.window.bordered(),
+          documentation = cmp.config.window.bordered(),
+        },
+        mapping = cmp.mapping.preset.insert({
+          ["<C-b>"] = cmp.mapping.scroll_docs(-4),
+          ["<C-f>"] = cmp.mapping.scroll_docs(4),
+          ["<C-Space>"] = cmp.mapping.complete(),
+          ["<C-e>"] = cmp.mapping.abort(),
+          ["<CR>"] = cmp.mapping.confirm({ select = true }),
+        }),
+        sources = cmp.config.sources({
+          {
+            name = "nvim_lsp",
+            entry_filter = function(entry)
+              return require("cmp.types").lsp.CompletionItemKind[entry:get_kind()] ~= "Text"
+            end,
+          },
+          { name = "luasnip" },
+        }, {
+          { name = "buffer" },
+        }),
+      })
+    end,
+  },
+  {
+    "hrsh7th/cmp-nvim-lsp",
+  },
+  {
+    "L3MON4D3/LuaSnip",
+    dependencies = {
+      "saadparwaiz1/cmp_luasnip",
+      "rafamadriz/friendly-snippets",
+    },
+  },
+}