feat: add doc-freshness agentic workflow (#190)

* feat: add doc-freshness agentic workflow

Adds a weekly GitHub agentic workflow that detects documentation drift
by comparing recent source changes against documentation. The agent:

- Reads commits since last time workflow ran (or last 7 days)
- Compares CLI --help output against README/docs
- Files up to 2 advisory [Doc Drift] issues (deduplicated by title), no issue created if no drift found. group drift issues by area (max 2: source + docs). 
- Labels: type:documentation, 
- Fire-and-forget: no auto-assign, no reminders, no auto-close (but subject to stale item workflow like any other issue)

Human gate is post-hoc: maintainer reviews each filed issue and either creates a docs-update PR or closes with docs:no-action-needed.

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: 3 people

.gitattributes

@@ -3,3 +3,5 @@
 .squad/agents/*/history.md merge=union
 .squad/log/** merge=union
 .squad/orchestration-log/** merge=union
+
+.github/workflows/*.lock.yml linguist-generated=true merge=ours

.github/aw/actions-lock.json

@@ -0,0 +1,9 @@
+{
+  "entries": {
+    "github/gh-aw-actions/setup@v0.80.9": {
+      "repo": "github/gh-aw-actions/setup",
+      "version": "v0.80.9",
+      "sha": "8c7d04ebf1ece56cd381446125da3e0f6896294a"
+    }
+  }
+}