Replace Python endpoint-discovery with --discover flag (replaces #936)

- Add --discover and --discover-output to unpoller; uses first unifi
  controller from config to probe known API endpoints and write a
  shareable markdown report.
- Add Discoverer interface and RunDiscover(); inputunifi implements
  Discoverer via unifi.DiscoverEndpoints.
- Remove tools/endpoint-discovery/ (Python/Playwright).
- Add docs/PR_936_REPLACEMENT.md. .gitignore: test config and report.

Requires unpoller/unifi with DiscoverEndpoints (replace in go.mod until
unifi release).

pkg/poller/inputs.go

@@ -24,6 +24,12 @@ type Input interface {
 	DebugInput() (bool, error)
 }
 
+// Discoverer is an optional interface for inputs that can discover API endpoints
+// on a controller and write a shareable report (e.g. for support/debugging).
+type Discoverer interface {
+	Discover(outputPath string) error
+}
+
 // InputPlugin describes an input plugin's consumable interface.
 type InputPlugin struct {
 	Name   string