feat(resolve): add resolve command and log integration (#125)

Add first-class conflict resolution support to jj.nvim.

   - add `jj.cmd.resolve` to run `jj resolve` in a floating terminal or via an
     external tool
   - add `:J resolve` with support for `-r/--revision`, `--tool`,
     `--external/--ext`, and positional filesets
   - integrate resolve into the log buffer with the `gr` mapping and optional
     `resolve_strategies` picker
   - add `utils.is_change_conflicted()` and avoid opening resolve when the
     selected revision has no conflicts
   - document resolve usage, config, and keymaps in the README
   - add tests for resolve arg parsing and conflict detection helpers

lua/jj/core/runner.lua

@@ -17,7 +17,8 @@ end
 --- @return boolean success Whether the command succeeded
 function M.execute_command(cmd, error_prefix, input, silent)
 	local stderr_file = vim.fn.tempname()
-	local output = vim.fn.system({ "sh", "-c", string.format("(%s) 2>%s", cmd, vim.fn.shellescape(stderr_file)) }, input)
+	local output =
+		vim.fn.system({ "sh", "-c", string.format("(%s) 2>%s", cmd, vim.fn.shellescape(stderr_file)) }, input)
 	local success = vim.v.shell_error == 0
 
 	if not success then