feat(v2): T-309 SQLite fall-event persistence (mattn/go-sqlite3)

Persist confirmed fall events to a local SQLite DB under artifacts/:
camera host/port/channel + event id/track/source/config version/state/
latency/screenshot path/confirmed-at. Schema stores no password (guarded
by test). Wire openRecorder/saveRecord into the alerts loop; failures are
non-fatal. Re-applied the SILVER-POSE vendored os_windows.go patch that
go mod vendor reverted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v2/vendor/github.com/mattn/go-sqlite3/.gitignore

@@ -0,0 +1,14 @@
+*.db
+*.exe
+*.dll
+*.o
+
+# VSCode
+.vscode
+
+# Exclude from upgrade
+upgrade/*.c
+upgrade/*.h
+
+# Exclude upgrade binary
+upgrade/upgrade