feat(config_flow): digit-delay (0.05–1.0 s, invalid input error) + optional send-enter options UI consumed by the §7 channel path; strings/README updated (P5-2.1)

README.md

@@ -84,6 +84,14 @@ TV Remote entity, the Nvidia Remote Protocol (PIN pairing), or ADB
 media-session mode (ADB enabled + host). The `no_state_source` form error
 fires only when none of the three is present; ADB-only setups are valid.
 
+### Channel entry options
+
+The options flow exposes the §7 channel behavior the integration replicates:
+the inter-digit **delay** (0.05–1.0 s, default 0.1) and the optional
+**ENTER press** after the digits (off by default — TiviMate's validated
+behavior). Both are consumed by `play_media` with
+`media_content_type: channel`.
+
 ### Raw `adb_command` service (opt-in)
 
 When enabled in the integration's options (`adb_command_enabled`, **default