[log] log: add debug logging to server/difc_log (#2228)

Adds a `logDifcLog` debug logger (`"server:difc_log"` namespace) to
`internal/server/difc_log.go` and instruments the three key functions
with 5 meaningful debug logging calls.

## Changes

**File:** `internal/server/difc_log.go`

- Added `var logDifcLog = logger.New("server:difc_log")` (reuses the
existing `logger` import)
- `logFilteredItems`: logs filtered item count at entry (`serverID`,
`toolName`, `count`)
- `buildFilteredItemLogEntry`: logs extracted DIFC labels
(`description`, `secrecy`, `integrity`) and item metadata (`author`,
`number`, `URL`) when available
- `buildDIFCFilteredNotice`: logs filtered item count and which notice
format branch is selected (per-item detail vs. summary-only)

## Why this file

`difc_log.go` contains the DIFC filtering pipeline's logging and
notice-building logic. Understanding *how many* items are being
filtered, *what labels* they carry, and *which code path* the notice
builder takes is critical when debugging integrity policy violations.
The existing operational logging (via `logger.LogInfoWithServer`)
records the outcome; these debug logs trace the control flow that
produces it.

## Usage

```bash
# Enable debug logs for this file only
DEBUG=server:difc_log ./awmg --config config.toml

# Enable all server debug logs
DEBUG=server:* ./awmg --config config.toml
```

All log calls are zero-overhead when `DEBUG` does not match the
namespace.




> Generated by [Go Logger
Enhancement](https://github.com/github/gh-aw-mcpg/actions/runs/23350545859)
·
[◷](https://github.com/search?q=repo%3Agithub%2Fgh-aw-mcpg+%22gh-aw-workflow-id%3A+go-logger%22&type=pullrequests)

<!-- gh-aw-agentic-workflow: Go Logger Enhancement, engine: copilot, id:
23350545859, workflow_id: go-logger, run:
https://github.com/github/gh-aw-mcpg/actions/runs/23350545859 -->

<!-- gh-aw-workflow-id: go-logger -->

Author: lpcox

internal/server/difc_log.go

@@ -9,11 +9,14 @@ import (
 	"github.com/github/gh-aw-mcpg/internal/logger"
 )
 
+var logDifcLog = logger.New("server:difc_log")
+
 // logFilteredItems logs structured details for every item removed by DIFC filtering.
 // Each item is written as a [DIFC-FILTERED] JSON entry to both the unified and
 // per-server text log files (via LogInfoWithServer), and as a DIFC_FILTERED entry
 // in the JSONL log.
 func logFilteredItems(serverID, toolName string, filtered *difc.FilteredCollectionLabeledData) {
+	logDifcLog.Printf("Logging filtered items: serverID=%s, toolName=%s, count=%d", serverID, toolName, len(filtered.Filtered))
 	for _, detail := range filtered.Filtered {
 		entry := buildFilteredItemLogEntry(serverID, toolName, detail)
 		b, err := json.Marshal(entry)
@@ -39,6 +42,7 @@ func buildFilteredItemLogEntry(serverID, toolName string, detail difc.FilteredIt
 		entry.Description = detail.Item.Labels.Description
 		entry.SecrecyTags = difc.TagsToStrings(detail.Item.Labels.Secrecy.Label.GetTags())
 		entry.IntegrityTags = difc.TagsToStrings(detail.Item.Labels.Integrity.Label.GetTags())
+		logDifcLog.Printf("Filtered item labels: description=%s, secrecy=%v, integrity=%v", entry.Description, entry.SecrecyTags, entry.IntegrityTags)
 	}
 
 	// Extract identifying metadata from the raw item data.
@@ -49,6 +53,7 @@ func buildFilteredItemLogEntry(serverID, toolName string, detail difc.FilteredIt
 		entry.HTMLURL = getStringField(m, "html_url", "htmlUrl")
 		entry.Number = extractNumberField(m)
 		entry.SHA = getStringField(m, "sha")
+		logDifcLog.Printf("Filtered item metadata: author=%s, number=%s, url=%s", entry.AuthorLogin, entry.Number, entry.HTMLURL)
 	}
 
 	return entry
@@ -117,8 +122,11 @@ func buildDIFCFilteredNotice(filtered *difc.FilteredCollectionLabeledData) strin
 		return ""
 	}
 
+	logDifcLog.Printf("Building DIFC filtered notice: filteredCount=%d, maxInline=%d", n, maxFilteredItemsInNotice)
+
 	// For a small number of filtered items, include per-item descriptions and reasons.
 	if n <= maxFilteredItemsInNotice {
+		logDifcLog.Printf("Using per-item notice format for %d item(s)", n)
 		parts := make([]string, 0, n)
 		for _, detail := range filtered.Filtered {
 			desc := ""