fix: show absolute path instead of ??? when globally linking from cwd (#10899)

When running `pnpm add -g .`, the linked-from path equals the cwd,
so path.relative() returns an empty string which is falsy, causing
the fallback to '???'. Use the absolute path as fallback instead.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.changeset/fix-global-link-output.md

@@ -0,0 +1,6 @@
+---
+"@pnpm/default-reporter": patch
+"pnpm": patch
+---
+
+Fixed global install output showing `???` instead of the linked package path when linking from the current directory.

cli/default-reporter/src/reporterForClient/reportSummary.ts

@@ -118,7 +118,7 @@ function printDiffs (
       result += ` ${chalk.red('deprecated')}`
     }
     if (pkg.from) {
-      result += ` ${chalk.grey(`<- ${pkg.from && path.relative(opts.prefix, pkg.from) || '???'}`)}`
+      result += ` ${chalk.grey(`<- ${path.relative(opts.prefix, pkg.from) || pkg.from}`)}`
     }
     if (pkg.added && depType === 'dev' && opts.pnpmConfig?.saveDev === false && opts.cmd === 'add') {
       result += `${chalk.yellow(' already in devDependencies, was not moved to dependencies.')}`