feat(agent-mail): Add Python adapter library for Agent Mail integration

- Created lib/beads_mail_adapter.py with AgentMailAdapter class
- Automatic health check on initialization
- Graceful degradation when server unavailable
- Methods: reserve_issue(), release_issue(), notify(), check_inbox()
- Environment-based configuration (AGENT_MAIL_URL, AGENT_MAIL_TOKEN)
- Comprehensive unit tests (15 tests, 100% passing)
- Full documentation in lib/README.md

Closes bd-m9th

Amp-Thread-ID: https://ampcode.com/threads/T-caa26228-0d18-4b35-b98a-9f95f6a099fe
Co-authored-by: Amp <amp@ampcode.com>

scripts/simple_latency_test.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Simple latency benchmark for bd-htfk
+set -e
+
+echo "# Latency Benchmark Results"
+echo ""
+echo "## Git Sync Latency Test (10 runs)"
+echo ""
+
+# Test git sync latency
+for i in {1..10}; do
+    start=$(date +%s%N)
+    
+    # Create, update, and sync an issue
+    test_id=$(bd create "Latency test $i" -p 3 --json 2>/dev/null | jq -r '.id')
+    bd update "$test_id" --status in_progress >/dev/null 2>&1
+    bd sync >/dev/null 2>&1
+    
+    end=$(date +%s%N)
+    latency_ms=$(((end - start) / 1000000))
+    
+    echo "Run $i: ${latency_ms}ms"
+    
+    # Cleanup
+    bd close "$test_id" --reason "test" >/dev/null 2>&1
+done
+
+echo ""
+echo "## Notes"
+echo "- Git sync includes: create → update → export → commit → push → pull → import"
+echo "- This represents the full round-trip time for issue changes to sync via git"
+echo "- Agent Mail latency test skipped (server not running)"
+echo "- Expected git latency: 1000-5000ms"
+echo "- Expected Agent Mail latency: <100ms (when server running)"