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/config.go

@@ -68,12 +68,14 @@ type UnifiPoller struct {
 
 // Flags represents the CLI args available and their settings.
 type Flags struct {
-	ConfigFile string
-	DumpJSON   string
-	HashPW     string
-	ShowVer    bool
-	DebugIO    bool
-	Health     bool
+	ConfigFile     string
+	DumpJSON       string
+	HashPW         string
+	ShowVer        bool
+	DebugIO        bool
+	Health         bool
+	Discover       bool
+	DiscoverOutput string
 	*pflag.FlagSet
 }