Add text-to-speech via Piper TTS

Send text message → Piper TTS → WAV → OGG Opus → voice reply.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/telegram.zig

@@ -15,6 +15,7 @@ pub const VideoNote = struct {
 pub const Message = struct {
     message_id: i64,
     chat: struct { id: i64 },
+    text: ?[]const u8 = null,
     voice: ?Voice = null,
     video_note: ?VideoNote = null,
 };
@@ -134,4 +135,35 @@ pub const TelegramBot = struct {
         const resp = http.httpPostJson(self.allocator, url, json_body) catch return;
         self.allocator.free(resp);
     }
+
+    pub fn sendVoice(self: *TelegramBot, chat_id: i64, ogg_path: []const u8, reply_to: ?i64) !void {
+        const url = try std.fmt.allocPrint(self.allocator, "{s}/sendVoice", .{self.api_base});
+        defer self.allocator.free(url);
+
+        const chat_id_str = try std.fmt.allocPrint(self.allocator, "{d}", .{chat_id});
+        defer self.allocator.free(chat_id_str);
+
+        var fields_buf: [2][2][]const u8 = undefined;
+        var field_count: usize = 1;
+        fields_buf[0] = .{ "chat_id", chat_id_str };
+
+        var reply_str: ?[]u8 = null;
+        defer if (reply_str) |s| self.allocator.free(s);
+
+        if (reply_to) |r| {
+            reply_str = try std.fmt.allocPrint(self.allocator, "{d}", .{r});
+            fields_buf[1] = .{ "reply_to_message_id", reply_str.? };
+            field_count = 2;
+        }
+
+        const resp = try http.httpPostMultipart(
+            self.allocator,
+            url,
+            "voice",
+            ogg_path,
+            "voice.ogg",
+            fields_buf[0..field_count],
+        );
+        self.allocator.free(resp);
+    }
 };