refactor(status-line): omit Errors/Warnings/Info tags when the count is zero

The happy-path status line always carried `| Errors: 0 | Warnings: 0
| Info: 0 |` even for a clean command with nothing to report. Those
nine tokens per call paid for zero information — if the AI needed to
know "was there an error", the status icon (✓ vs ✗) already answered
that. The tags only earn their keep when the count is > 0.

Match the discipline the same format already uses for `| Pipeline:
...` (which is omitted when the pipeline summary is empty): each of
the three counters is now only emitted when its value is positive.

Before (happy path):
  ✓ Pipeline executed successfully | Window: #12345 Cat | Status: Ready | Pipeline: Get-Date | Duration: 0.20s | Errors: 0 | Warnings: 0 | Info: 0 | Location [FileSystem]: C:\...

After (happy path):
  ✓ Pipeline executed successfully | Window: #12345 Cat | Status: Ready | Pipeline: Get-Date | Duration: 0.20s | Location [FileSystem]: C:\...

Before (1 error, 0 warnings, 0 info):
  ✗ ... | Duration: 0.20s | Errors: 1 | Warnings: 0 | Info: 0 | Location ...

After (1 error, 0 warnings, 0 info):
  ✗ ... | Duration: 0.20s | Errors: 1 | Location ...

Before (0 errors, 1 warning, 3 info):
  ✓ ... | Duration: 0.20s | Errors: 0 | Warnings: 1 | Info: 3 | Location ...

After (0 errors, 1 warning, 3 info):
  ✓ ... | Duration: 0.20s | Warnings: 1 | Info: 3 | Location ...

Parser impact: consumers that currently pattern-match `Errors: N` are
unaffected (the pattern still matches when N > 0, and the case that
was silently satisfied by "Errors: 0" is now silently satisfied by
tag absence — which any sensible parser was already treating as 0).
No tests in the repo asserted literal `Errors: 0` / `Warnings: 0` /
`Info: 0` on a status line, so the existing 251-test suite needs no
changes.

Author: yotsuda

PowerShell.MCP/Resources/MCPPollingEngine.ps1

@@ -351,7 +351,17 @@ if (-not (Test-Path Variable:global:McpTimer)) {
                 $windowTitle = $Host.UI.RawUI.WindowTitle
 
                 $pipelineInfo = if ($pipelineSummary) { " | Pipeline: $pipelineSummary" } else { "" }
-                $statusLine = "$statusIcon Pipeline $statusText | Window: $windowTitle | Status: $Status$pipelineInfo | Duration: $durationText | Errors: $errorCount | Warnings: $warningCount | Info: $infoCount | $LocationInfo"
+                # Zero-count tags (Errors: 0 / Warnings: 0 / Info: 0) are
+                # silent on the happy path — a clean run produces a
+                # shorter status line and a run with actual events
+                # produces a line where every count listed is non-zero
+                # by construction. This follows the same "omit what
+                # equals zero" discipline the status line already uses
+                # for `$pipelineInfo`.
+                $errInfo  = if ($errorCount   -gt 0) { " | Errors: $errorCount" }    else { "" }
+                $warnInfo = if ($warningCount -gt 0) { " | Warnings: $warningCount" } else { "" }
+                $infoInfo = if ($infoCount    -gt 0) { " | Info: $infoCount" }       else { "" }
+                $statusLine = "$statusIcon Pipeline $statusText | Window: $windowTitle | Status: $Status$pipelineInfo | Duration: $durationText$errInfo$warnInfo$infoInfo | $LocationInfo"
 
                 # Generate structured output strings
                 $structuredOutput = @{