nixvim: improve keymaps, completion, and formatter config

- Add LSP code actions, diagnostic navigation, window navigation keymaps
- Move telescope keymaps to explicit mkRaw form for reliability
- Change buffer nav from <leader>bh/bl to [b/]b
- Fix conform double-setup by moving config to native nixvim settings
- Fix <leader>cf to use conform instead of vim.lsp.buf.format
- Fix <leader>ca to pass diagnostic context to code_action
- Add nvim-lightbulb for code action indicator
- Configure copilot Tab conflict: blink-cmp Tab=accept, C-n/p for cycling
- Add completion.list.selection preselect for immediate Tab acceptance
- Add TypeScript Japanese locale for LSP diagnostics

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

modules/home/nixvim/default.nix

@@ -40,25 +40,5 @@
       nixd
     ];
 
-    extraConfigLua = ''
-      require("conform").setup({
-        formatters_by_ft = {
-          javascript = { "prettierd", "prettier", stop_after_first = true },
-          javascriptreact = { "prettierd", "prettier", stop_after_first = true },
-          typescript = { "prettierd", "prettier", stop_after_first = true },
-          typescriptreact = { "prettierd", "prettier", stop_after_first = true },
-          json = { "prettierd", "prettier", stop_after_first = true },
-          yaml = { "prettierd", "prettier", stop_after_first = true },
-          markdown = { "prettierd", "prettier", stop_after_first = true },
-          lua = { "stylua" },
-          nix = { "alejandra" },
-          sh = { "shfmt" },
-        },
-        format_on_save = function(_)
-          return { timeout_ms = 1000, lsp_format = "fallback" }
-        end,
-      })
-
-    '';
   };
 }